ENGINEERING  LIBRARY 


INDUSTRIAL 
HYDROGEN 


BY 

HUGH  S.  TAYLOE,  D.Sc. 

ASSOCIATE   PROFESSOR   OP   PHYSICAL   CHEMISTRY, 
PRINCETON   UNIVERSITY 


American  Chemical  Society 
Monograph  Series 


BOOK  DEPARTMENT 
The  CHEMICAL  CATALOG  COMPANY,  Inc. 

ONE  MADISON  AVENUE,  NEW  YORK,  U.  S.  A. 
1921 


COPYRIGHT,  1921,  BY 
The  CHEMICAL  CATALOG  COMPANY,  Inc. 

All  Rights  Reserved 


Press  of 

J.  J.  Little  &  Ives  Company 
New  York,  U.  S.  A. 


£& 


GENEKAL  INTRODUCTION 

American  Chemical  Society  Series  of 
Scientific  and  Technologic  Monographs 

By  arrangement  with  the  Interallied  Conference  of  Pure  and 
Applied  Chemistry,  which  met  in  London  and  Brussels  in  July, 
1919,  the  American  Chemical  Society  was  to  undertake  the  pro- 
duction and  publication  of  Scientific  and  Technologic  Mono- 
graphs on  chemical  subjects.  At  the  same  time  it  was  agreed 
that  the  National  Research  Council,  in  cooperation  with  the 
American  Chemical  Society  and  the  American  Physical  Society, 
should  undertake  the  production  and  publication  of  Critical 
Tables  of  Chemical  and  Physical  Constants.  The  American 
Chemical  Society  and  the  National  Research  Council  mutually 
agreed  to  care  for  these  two  fields  of  chemical  development.  The 
American  Chemical  Society  ;najned  as  Trustees,  to  make  the  nec- 
essary arrangements  for  the  publication  of  the  monographs, 
Charles  L.  Parsons,  Secretary  of  the  American  Chemical  Society, 
Washington,  D.  C.;  John  E.  Teeple,  Treasurer  of  the  American 
Chemical  Society,  New  York  City;  and  Professor  Gellert  Alle- 
man  of  Swarthmore  College.  The  Trustees  have  arranged  for 
the  publication  of  the  American  Chemical  Society  series  of  (a) 
Scientific  and  (b)  Technologic  Monographs  by  the  Chemical 
Catalog  Company  of  New  York  City. 

The  Council,  acting  through  the  Committee  on  National  Pol- 
icy of  the  American  Chemical  Society,  appointed  the  editors, 
named  at  the  close  of  this  introduction,  to  have  charge  of  secur- 
ing authors,  and  of  considering  critically  the  manuscripts  pre- 
pared. The  editors  of  each  series  will  endeavor  to  select  topics 
which  are  of  current  interest  and  authors  who  are  recognized  as 
authorities  in  their  respective  fields.  The  list  of  monographs  thus 
far  secured  appears  in  the  publisher's  own  announcement  else- 
where in  this  volume. 

The  development  of  knowledge  in  all  branches  of  science,  and 

3 


M504990 


4  GENERAL  INTRODUCTION 

especially  in  chemistry,  has  been  so  rapid  during  the  last  fifty 
years  and  the  fields  covered  by  this  development  have  been  so 
varied  that  it  is  difficult  for  any  individual  to  keep  in  touch  with 
the  progress  in  branches  of  science  outside  his  own  specialty. 
In  spite  of  the  facilities  for  the  examination  of  the  literature 
given  by  Chemical  Abstracts  and  such  compendia  as  Beilstein's 
Handbuch  der  Organischen  Chemie,  Richter's  Lexikon,  Ostwald's 
Lehrbuch  der  Allgemeinen  Chemie,  Abegg's  and  Gmelin-Kraut's 
Handbuch  der  Anorganischen  Chemie  and  the  English  and 
French  Dictionaries  of  Chemistry,  it  often  takes  a  great  deal  of 
time  to  coordinate  the  knowledge  available  upon  a  single  topic. 
Consequently  when  men  who  have  spent  years  in  the  study  of 
important  subjects  are  willing  to  coordinate  their  knowledge 
and  present  it  in  concise,  readable  form,  they  perform  a  service 
of  the  highest  value  to  their  fellow  chemists. 

It  was  with  a  clear  recognition  of  the  usefulness  of  reviews 
of  this  character  that  a  Committee  of  the  American  Chemical 
Society  recommended  the  publication  of  the  two  series  of  mono- 
graphs under  the  auspices  of  the  Society. 

Two  rather  distinct  purposes  are  to  be  served  by  these  mono- 
graphs. The  first  purpose,  whose  fulfilment  will  probably  render 
to  chemists  in  general  the  most  important  service,  is  to  present 
the  knowledge  available  upon  the  chosen  topic  in  a  readable 
form,  intelligible  to  those  whose  activities  may  be  along  a  wholly 
different  line.  Many  chemists  fail  to  realize  how  closely  their 
investigations  may  be  connected  with  other,  work  which  on  the 
surface  appears  far  afield  from  their  own.  These  monographs 
will  enable  such  men  to  form  closer  contact  with  the  work  of 
chemists  in  other  lines  of  research.  The  second  purpose  is  to 
promote  research  in  the  branch  of  science  covered  by  the  mono- 
graph, by  furnishing  a  well  digested  survey  of  the  progress  al- 
ready made  in  that  field  and  by  pointing  out  directions  in  which 
investigation  needs  to  be  extended.  To  facilitate  the  attain- 
ment of  this  purpose,  it  is  intended  to  include  extended  references 
to  the  literature,  which  will  enable  anyone  interested  to  follow 
up  the  subject  in  more  detail.  If  the  literature  is  so  voluminous 
that  a  complete  bibliography  is  impracticable,  a  critical  selec- 
tion will  be  made  of  those  papers  which  are  most  important. 

The  publication  of  these  books  marks  a  distinct  departure  in 
the  policy  of  the  American  Chemical  Society  inasmuch  as  it  is  a 


GENERAL  INTRODUCTION  5 

serious  attempt  to  found  an  American  chemical  literature  with- 
out primary  regard  to  commercial  considerations.  The  success 
of  the  venture  will  depend  in  large  part  upon  the  measure  of  co- 
operation which  can  be  secured  in  the  preparation  of  books  deal- 
ing adequately  with  topics  of  general  interest;  it  is  earnestly 
hoped,  therefore,  that  every  member  of  the  various  organizations 
in  the  chemical  and  allied  industries  will  recognize  the  impor- 
tance of  the  enterprise  and  take  sufficient  interest  to  justify  it. 


AMERICAN   CHEMICAL   SOCIETY 

BOARD   OF   EDITORS 

Scientific  Series: —  Technologic  Series: — 

WILLIAM  A.  NOTES,  Editor,         JOHN  JOHNSTON,  Editor, 
GILBERT  N.  LEWIS,  C.  G.  DERICK, 

LAFAYETTE  B.  MENDEL,  WILLIAM  HOSKINS, 

ARTHUR  A.  NOYES,  F.  A.  LIDBURY, 

JULIUS  STIEGLITZ.  ARTHUR  D.  LITTLE, 

C.  L.  REESE, 
C.  P.  TOWNSEND. 


American  Chemical  Society 

MONOGRAPH   SERIES 

Other  monographs  in  the  series  of  which  this  book  is  a  part 
are  now  ready  or  in  process  of  being  printed  or  written.  They 
will  be  uniform  in  size  and  style  of  binding.  The  list  up  to 
July  First,  1921,  includes: 

Organic  Compounds  of  Mercury. 

By  FRANK  C.  WHITMORE.    397  pages.    Price  $4.50. 
The  Chemistry  of  Enzyme  Actions. 

By  K.  GEORGE  FALK.    140  pages.    Price  $2.50. 

The  Chemical  Effects  of  Alpha  Particles  and  Electrons. 
By  SAMUEL  C.  LIND.    180  pages.    Price  $3.00. 

The  Animal  as  a  Converter. 

By  HENRY  PRENTISS  ARMSBY. 
The  Properties  of  Electrically  Conducting  Systems. 

By  CHARLES  A.  KRAUS.    About  400  pages,  illustrated. 
Carotinoids  and  Related  Pigments :  The  Chromolipins. 

By  LEROY  S.  PALMER.    About  200  pages,  illustrated. 
Thyroxin.      By  E.  C.  KENDALL. 
The  Properties  of  Silica  and  the  Silicates. 

By  ROBERT  S.  SOSMAN.    About  500  pages,  illustrated. 
Coal  Carbonization.     By  HORACE  C.  PORTER. 
The  Corrosion  of  Alloys.     By  C.  G.  FINK. 
The  Vitamines.    By  H.  C.  SHERMAN.    About  200  pages. 
Piezo-Chemistry.   By  L.  H.  ADAMS.    About  350  pages. 
Cyanamide.    By  JOSEPH  M.  BRAHAM. 
Liquid  Ammonia  as  a  Solvent.     By  E.  C.  FRANKLIN. 
Wood  Distillation.      By  L.  F.  HAWLEY. 
Shale  On.    By  RALPH  H.  McKEE. 

Aluminothermic  Reduction  of  Metals.  By  B.  D.  SAKLAT- 
WALLA. 

The  Analysis  of  Rubber.     By  JOHN  B.  TUTTLE. 
Zirconium    and    Its     Compounds.      By  F.  P.  VENABLE. 
The    Chemistry    of    Leather    Manufacture.     By  JOHN 
A.  WILSON.    About  400  to  500  pages. 

For  additional  information  regarding  this  series  of  monographs,  see 
General  Introduction,  page  3.  As  the  number  of  copies  of  any  one 
monograph  will  be  limited,  advance  orders  are  solicited. 

The  CHEMICAL  CATALOG  COMPANY,  Inc. 

ONE  MADISON  AVENUE,  NEW  YORK,  U.  S.  A. 


AUTHOR'S  PREFACE 

The  present  monograph  outlines  the  fundamental  principles 
and  essential  chemical  facts  of  the  industry  of  hydrogen  produc- 
tion. It  attempts  to  trace  the  steps  by  which  the  present  status 
of  the  industry  has  been  reached,  to  detail  what  that  present 
status  is  and  what  lines  of  future  development  may  be  antici- 
pated. The  two- fold  purpose  of  the  monograph  series,  as  out- 
lined by  the  Board  of  Editors,  has  been  kept  steadily  in  mind. 
It  is  hoped  that  a  readable  account  has  been  given  of  available 
knowledge  and  £hat,  in  many  directions,  the  necessity  for  more 
research  and  experimental  investigation  has  been  indicated. 

Modern  chemical  technology  demands  the  intelligent  co- 
operation of  the  chemist  and  the  engineer.  The  attempt  to  elimi- 
nate the  one  or  the  other  from  the  development  of  a  new  process, 
generally  results  in  retarded  progress.  Nor  is  anything  gained 
by  the  intrusion  of  the  one  into  the  legitimate  field  of  the  other; 
indeed,  the  results  of  such  intrusion  are,  quite  frequently,  ludi- 
crous. Consequently,  the  chemical  side  of  the  problems  of  hydro- 
gen technology  is  here  emphasized.  It  is  thought,  however,  that 
the  necessary  data  have  been  supplied  upon  which  an  engineering 
staff  could  readily  base  its  calculations  for  actual  plant  details. 

The  problem  of  cost  factors  in  a  technical  monograph  is  a 
difficult  one,  upon  which  most  diverse  views  are  current.  No 
extended  discussion  of  costs  is  to  be  found  in  the  following  pages, 
a  decision  which  was  reached  as  a  result  of  the  rapidly  varying 
prices  in  fuel,  labor  and  machinery  in  recent  years  and  of  the 
varying  factors  of  cost,  arising  from  location  of  plant  and  avail- 
ability and  selling  costs  of  the  by-products  of  several  hydrogen 
processes.  It  has  been  attempted,  however,  to  supply  in  all  cases 
the  necessary  data  upon  which  such  cost  calculations  can  be 
made.  Indeed,  such  an  exercise  has  been  undertaken  and  carried 
through  several  times  in  'recent  years,  in  varying  circumstances, 
with  the  data  here  assembled. 

The  monograph  differs  in  size  and  in  plan  from  those  books 

7 


8  AUTHOR'S  PREFACE 

dealing  with  the  subject  which  have  preceded  it.  The  literature 
of  the  subject  has  been  critically  examined  and,  in  the  light  of 
accumulated  knowledge,  much  that  has  been  previously  claimed, 
in  patents  and  otherwise,  has  been  discarded  as  impracticable. 
The  monograph  resembles  most  closely  the  chapter  on  hydrogen 
by  the  late  Dr.  A.  C.  Greenwood  in  his  excellent  "Industrial 
Gases,"  but  opportunity  for  much  fuller  treatment  has  been  avail- 
able in  the  present  case.  Ideas  and  information  have  been  ob- 
tained from  a  perusal  of  other  volumes,  including  the  works  of 
Ellis,  "Hydrogenation  of  Oils,"  Teed,  "The  Chemistry  and  Manu- 
facture of  Hydrogen"  and  the  British  Admiralty  "Hydrogen 
Manual,"  in  two  volumes,  which  deal  intensively  with  two  pro- 
cesses, the  silicol  and  the  steam-iron  process.  From  the  chemical 
literature,  help  in  the  form  of  articles  and  drawings  has  been 
obtained.  These  are  acknowledged  in  the  text.  The  electrolytic 
hydrogen  industry,  and  especially  the  Electrolabs  Co.  and  the 
International  Oxygen  Co.,  have  placed  material  unstintingly  at 
my  disposal.  It  is  a  pleasure  to  record  the  assistance  which  many 
of  my  friends  have  given  me  in  discussing  points  which  appeared 
to  be  debatable.  To  the  General  Editor,  Dr.  John  Johnston,  and 
to  Messrs.  R.  S.  Tour  and  G.  0.  Carter,  from  all  of  whom  sug- 
gestions have  been  received  and  accepted,  my  best  thanks  are  due. 
My  wife  has  lightened  the  clerical  labours  which  inevitably  accrue 
to  such  an  undertaking.  She  has  my  generous  appreciation. 
Oct.  1,  1921. 


CONTENTS 

PAGE 

CHAPTER  I.    INTRODUCTION 15 

Growth  of  the  Industry.  Uses  of  Hydrogen.  Sources 
of  Hydrogen  Supply.  Classification  of  Systems  of 
Production.  Choice  of  Process.  Safety  Precautions. 

CHAPTER  II.  HYDROGEN  FROM  STEAM  AND  IRON  ...  25 
Reactions  of  the  Process.  Historical.  The  Contact 
Mass.  Typical  Generator  Units.  Multi-retort  Type. 
Single-unit  Type.  Operational  Procedure.  The  Re- 
duction Phase.  The  Steaming  Period.  Aeration. 
Thermal  Balance  of  Process. 

CHAPTER  III.  HYDROGEN  FROM  WATER-GAS  AND  STEAM  .  60 
Theoretical.  The  Continuous  Water-Gas  Catalytic 
Process.  Outline.  Catalysts.  Operational  Details. 
Gas  Composition  Flow-sheets.  Plant  Details.  Fur- 
ther Purification:  Griesheim-Elektron  Process.  Out- 
line. Literature  Resume.  Mechanism  of  Reaction. 
Operational  Details:  Dieffenbach  and  Moldenhauer 
Process.  Outline.  Literature  Resume.  Mechanism  of 
Reaction. 

CHAPTER  IV.    HYDROGEN  FROM  WATER-GAS  BY  LIQUEFAC- 
TION     90 

Theoretical.  The  Linde-Frank-Caro  Process.  The 
Claude  Process.  Composition  of  Gas  Fractions.  Utili- 
sation of  Carbon  Monoxide  Fraction.  Plant  Details. 
General  Remarks.  Miscellaneous  Physical  Methods  of 
Preparation. 

CHAPTER  V.    HYDROGEN  BY  ELECTROLYSIS  ....    102 
Theoretical.     Energy   Factors.     Mechanism.     Early 
Forms  of  Apparatus.    Modern  Plants.    I.  0.  C.-Unit 

9 


10  CONTENTS 

PAGE 

Generator.  Levin  Cell.  Burdett  Cells.  High  Am- 
perage Units.  By-Product  Electrolytic  Hydrogen. 
Energy  Factors  in  Alkali-Chlorine  Cells.  Types  of 
Cells. 

CHAPTER  VI.    HYDROGEN  FROM  WATER      .        .        .        .     123 
The  Bergius  Process.    Description  of  Process.    General 
Discussion.    Field  Processes.    Metallic  Sodium  Proc- 
esses.   Hydrolith  Process.    Aluminium  Amalgam  Proc- 
esses. 

CHAPTER  VII.  HYDROGEN  FROM  AQUEOUS  ALKALIS  .  .  131 
The  Silicol  Process.  Outline.  Literature  Resume.  Ex- 
perimental Data.  Plant  Details.  Operational  Details. 
Ferro-Silicon  Specification.  Gas  Composition.  The 
Sludge  and  Its  Disposal.  General  Remarks  on  Effi- 
ciency and  Economy:  Aluminium-Sodium  Hydroxide 
Process. 

CHAPTER  VIII.    HYDROGEN  FROM  HYDROCARBONS      .        .     147 
Stability  of  Hydrocarbons.    Processes  of  Thermal  De- 
composition.   From  Coal-Gas.    From  Natural  Gas,  Pe- 
troleum and  Tar  Oils.    From  Acetylene.    Processes  of 
Interaction  with  Steam. 

CHAPTER  IX.    MISCELLANEOUS  AND  BY-PRODUCT  HYDRO- 
GEN PROCESSES 160 

The  Decomposition  of  Formates.  Hydrogen  from  De- 
hydrogenation  Processes.  Hydrogen  from  Fermenta- 
tion Processes.  Hydrogenite  Process.  Hydrogen  from 
Sulphides.  Hydrogen  from  Acids. 

CHAPTER  X.    THE  PURIFICATION  AND  TESTING  OF  HYDRO- 
GEN      171 

Purity  of  Commercial  Product.  Removal  of  Sulphur 
Compounds.  Removal  of  Carbon  Dioxide.  Removal 
of  Carbon  Monoxide.  Removal  of  Methane.  Removal 
of  Phosphine  and  Arsine.  Removal  of  Oxygen.  Re- 


CONTENTS  11 

moval  of  Water  Vapour.  Testing  of  Hydrogen.  Physi- 
cal Methods:  Effusion  Apparatus.  Thermal  Conduc- 
tivity Processes.  Gas  Interferometer.  Chemical  Meth- 
ods: Analysis  for  Carbon  Monoxide.  Analysis  for 
Oxygen.  Detection  and  Estimation  of  Phosphine,  Ar- 
sine,  Sulphuretted  Hydrogen  and  Acetylene. 

APPENDIX  I   .        .        .        ...        .        .        .        .    201 

INDEX  TO  AUTHORS        .        .        .        .        .  .        .    204 

INDEX  TO  SUBJECTS  207 


ILLUSTRATIONS 

SUBJECT 

NUMBER 
OF   FIG.  FAGK 

1.  Equilibria   in  the  System  Fe  -  FeO  -  H20  -  H2   and 

Fe304-FeO-H20-H2 26 

2.  Equilibria  in  the  System  Fe  -  FeO  -  CO  -  C02  and 

Fe3O4  -  FeO  -  CO  -  C02 27 

3.  (a)     Front  Elevation — Lane  Hydrogen  Retort  .        .      32 
(b)     Sectional  Plan — Lane  Hydrogen  Retort    .        .      33 

4.  Diagrammatic  Representation  of  Lane  Retort  Valve 

System    ..."      .        .        .       .       ,       ...      34 

5.  Single  Unit  Hydrogen  Retort — Grigg's  Design  .        .      39 

6.  Flow  Sheet  for  Water-Gas  Catalytic  Process     .        .  -     76 

7.  (a)     Diagrammatic  Outline  of  Converters  for  Water- 

Gas  Catalysis 78 

(b)     Detail  of  Gas  Flow  through  Inter  changers        .      78 

8.  Vapour  Pressure  Curves  of  Liquid  Nitrogen  and  Car- 

bon Monoxide.        .        .        .        .        .        ...      92 

9.  Diagrammatic  Representation  of  Linde  Liquefaction 

System .        .      94 

10.  Diagrammatic  Representation  of  Claude  Liquefaction 

System    . 95 

11.  International  Oxygen  Co.'s  Unit  Electrolytic  Gen- 

erator              .        .     113 

13 


14  ILLUSTRATIONS 

NUMBER 
OF   FIG.  PACK 

12.  Electrolabs  Levin  Hydrogen-Oxygen  Generator        .     116 

13.  Relation  of  Silicon  Content  to  Hydrogen  Yield  in 

Silicol  Process         .        .        .        .        .        .        .     133 

14.  Temperature — pressure — concentration    diagram    for 

alkali  solutions       .        .        .        .        .        .        .    135 

15.  Silicol  Process  Results        *        ...        .        .136 

16.  Equilibria  in  the  Systems  Fe-FeO-H20-H2,  Fe304- 
FeO-H20-H2,  FeFeO-CO-C02  and  Fe304-FeO-CO 
C02.  (Appendix  I) 201 


INDUSTRIAL  HYDROGEN 

Chapter  I. 
Introduction. 

The  production  of  hydrogen  on  a  large  scale  is  an  industrial 
development  of  the  last  two  decades.  Prior  to  1900  the  utilisation 
of  hydrogen  was  practically  confined  to  the  aeronautical  field, 
for  use  in  balloons,  and  to  a  few  minor  industrial  uses  such  as  for 
lead-burning,  the  working  of  platinum  metals  in  the  jewelry 
trade  and  the  production  of  light,  for  the  projection  of  pictures, 
by  the  burning  of  an  oxy-hydrogen  flame  in  contact  with  re- 
fractory oxides  such  as  lime.  In  the  main,  these  requirements 
were  satisfied  by  electrolytic  methods  of  production,  hydrogen 
and  oxygen  generally  being  simultaneously  produced.  For  the 
filling  of  balloons,  in  the  field  or  in  balloon  stations,  reliance 
was  placed  upon  hydrogen  produced  by  the  action  of  sulphuric 
acid  upon  iron  when  a  gas  of  greater  lifting  power  than  the  more 
usual  coal  gas  was  required. 

From  1900  onwards  the  demand  for  large  scale  hydrogen 
production  has  steadily  increased,  the  gas  now  occupying  a  very 
important  position  in  the  field  of  pure  gas  technology.  The  ad- 
vent of  the  dirigible  balloon  made  the  production  of  hydrogen 
imperative,  since,  by  its  use,  the  lifting  and  carrying  capacity  of 
the  airship  could  be  made  adequate  for  the  extra  weight  in- 
volved in  the  machinery,  fuel  and  men  employed  to  give  direc- 
tion to  the  vessel.  From  the  early  experimental  ships  of  Santos- 
Dumont,  through  the  laborious  trials  of  Zeppelin,  the  lighter- 
than-air  dirigible  has  evolved,  especially  during  recent  years, 
until  the  present  time.  The  dirigible  built  in  England  for  the 
United  States  Government  and  recently  destroyed  had  a  capacity 
of  2,700,000  cubic  feet  of  hydrogen. 

The  development  of  hydrogen  production  in  relation  to  dirig- 

15 


16  INDUSTRIAL  HYDROGEN 

ible  balloons  has  facilitated  also  the  developments  of  stationary 
or  kite  balloons,  as  emphasized  by  the  use  which  was  made  of 
such  in  recent  wars  for  purposes  of  reconnaissance. 

Paralleling  this  extraordinary  growth  in  the  field  of  aero- 
nautics, a  considerable  development  has  occurred  in  the  purely 
industrial  use  of  the  gas.  The  penetration  of  hydrogen  in  bulk 
into  the  industries  has  been  brought  about  by  the  technical  de- 
velopment of  catalytic  processes.  The  academic  studies  of  Saba- 
tier  and  his  co-workers x  in  the  catalytic  hydrogenation  of  organic 
compounds  by  means  of  base-metal  catalysts  such  as  nickel, 
cobalt,  copper  and  iron,  led  directly  to  the  establishment  of  the 
industry  of  hydrogenation  of  oils.  In  this  industry,  the  liquid 
glycerides  of  unsaturated  acids,  such  as  oleic  acid,  are  converted 
by  catalytic  hydrogenation  in  presence  of  nickel  or  other  catalyst 
into  the  solid  glycerides  of  saturated  acids,  such  as  stearic  acid. 
The  hardened  fats  are  made  use  of  extensively  in  the  production 
of  edible  products  and  also  in  the  soap  and  candle  industries.  It 
is  difficult  to  obtain  accurate  data  in  reference  to  the  present 
consumption  of  hydrogen  for  such  purposes.  It  may  safely  be 
stated,  however,  that  several  million  cubic  feet  of  hydrogen,  of 
high  purity,  are  daily  consumed,  in  this  country  alone,  for  such 
purposes. 

In  solving  the  problem  of  fixation  of  atmospheric  nitrogen  the 
role  of  hydrogen  production  has  assumed  first  importance.  The 
successful  development  of  ammonia  synthesis  in  Germany  and  its 
technical  operation  since  1913  has  entailed  a  tremendous  develop- 
ment of  hydrogen  manufacture.  The  production  of  one  ton 
(2,000  Ibs.)  of  fixed  nitrogen  as  ammonia  involves  the  theoretical 
consumption  of  approximately  430  pounds,  or  more  than  82,000 
cubic  feet,  of  hydrogen,  measured  at  ordinary  temperatures  and 
atmospheric  pressure.  The  hydrogen  consumption  of  the  Haber 
process  plants  in  Germany,  with  a  capacity  in  1918  of  650  metric 
tons  of  ammonia  per  day,2  will,  therefore,  readily  be  grasped.  For 
purposes  of  ammonia  synthesis  a  gas  of  high  purity  is  essential. 
Recent  developments  outside  of  Germany,  more  especially  in  con- 
nection with  the  high  pressure  process  of  M.  Georges  Claude  in 
France,  of  the  modified  Haber  process  of  the  General  Chemical 

1  La  Catalyse  en  Chimie  Orgamque,  2nd  Edition,  Sabatier.     Paris,  1020. 
*J.  Ind.  Eng.  Chem.t  1921,  13,  283. 


INTRODUCTION  17 

Company  in  this  country,  and  of  the  Nitrogen  Corporation  in 
England,  suggest  a  very  considerable  multiplication  of  hydrogen 
requirements  in  the  future  for  purposes  of  nitrogen  fixation  as 
ammonia. 

The  inevitable  cheapening  of  the  product,  which  results  from 
the  extended  scale  of  manufacture,  widens  the  field  of  possible 
technical  applications.  Already  in  use  for  catalytic  hydrogena- 
tion  in  the  fine  chemical  industry,  hydrogen  promises  to  find  ex- 
tended technical  application  in  other  catalytic  operations.  The 
production  of  pure  hydrogen  chloride  by  interaction  with  chlo- 
rine, the  hydrogenation  of  benzene  and  of  naphthalene  for  the 
production  of  hydrogenated  products  useful  as  fuels  or  solvents, 
the  reduction  of  nitrobenzene  in  the  vapor  or  liquid  phases  and 
the  conversion  of  acetaldehyde  to  alcohol  will  serve  as  indica- 
tions of  potential  hydrogen-consuming  processes  not  too  remote 
from  practical  industrial  use. 

Outside  the  catalytic  field  the  utilisation  of  hydrogen  has  also 
increased.  The  development  of  the  electric  filament  lamp  has 
resulted  in  a  large  demand  for  hydrogen.  The  gas  is  employed 
in  the  reduction  of  the  metallic  oxides,  in  the  working  up  of  the 
metals  into  filaments  and  in  the  displacement  of  air  from  the 
lamp  bulbs  prior  to  evacuation.  In  this  last  operation,  a  nitro- 
gen-hydrogen mixture  is  usually  employed.  As  in  the  metallurgy 
of  tungsten  for  the  lamp  industry,  so  with  other  rare  elements 
largely  in  use  for  alloy  purposes,  the  utilisation  of  hydrogen  as 
reducing  agent  eliminates  contamination  of  the  product  by  car- 
bon. 

The  use  of  the  oxy-hydrogen  flame  for  the  fusion  of  the  plati- 
num metals  is  well  known.  In  such  operations  the  presence  of 
carbon  is  avoided  owing  to  the  deleterious  effect  of  carbides  on 
the  properties  of  the  platinum  metals.  The  development,  how- 
ever, of  electric  furnaces  operating  in  absence  of  carbon  or  car- 
bon-containing gaseous  atmospheres,  as  for  example  the  Ajax- 
Northrup  electric  induction  furnace,  will  dimmish  the  utilisation 
of  hydrogen  for  such  purposes  and  may  also  have  an  influence  on 
the  use  of  hydrogen  in  the  non-platinum  rare-metal  industry. 

Of  minor  importance  in  the  question  of  hydrogen  utilisation 
is  the  artificial  gem  industry.  The  fusion  of  refractory  oxides 
such  as  alumina  in  presence  of  various  color-yielding  oxides, 


18  INDUSTRIAL  HYDROGEN 

as,  for  example,  chromic  oxide,  gives  synthetic  gems  such  as 
rubies,  sapphires  and  emeralds.  These  synthetic  gems  are,  how- 
ever, mainly  use  for  personal  adornment  and  the  tonnage  in- 
volved is  small.  Rubies  find  application,  nevertheless,  as  small 
bearings  for  delicate  mechanisms. 

The  Sources  of  Hydrogen  Supply. — Hydrogen  occurs  in  the 
free  state  in  minimal  quantities  only  in  nature.  Its  concentration 
in  the  atmosphere  certainly  does  not  exceed  0.02  per  cent.  In 
certain  natural  gas  supplies  a  higher  concentration  has  been  noted. 
For  example,  gas  in  the  Ohio  and  Indiana  fields  may  contain  0.5 
per  cent  of  hydrogen.  Since  the  gas  is  occluded  to  a  consider- 
able extent  by  certain  metals,  for  example,  the  platinum  metals, 
nickel,  iron  and  cobalt,  it  is  occasionally  present  in  large  per- 
centages in  the  gases  evolved  by  such  metals  found  in  nature 
in  the  elementary  condition.  Thus,  meteoric  iron  contains  oc- 
cluded gas  which  is  mainly  hydrogen.  This  is  not  surprising  when 
it  is  remembered  that  hydrogen  exists  uncombined  in  large  masses 
of  the  atmosphere  of  the  sun,  and  also  in  other  elements  of  the 
heavenly  bodies.  Violent  volcanic  eruptions  yield  gases  contain- 
ing free  hydrogen,  as  was  observed3  in  the  analyses  of  gases 
from  Kilauea,  where  the  concentration  was  approximately  10 
per  cent. 

In  the  combined  state,  on  the  other  hand,  hydrogen  is  ex- 
tremely abundantly  distributed  throughout  nature.  Not  only  is 
it  present  to  the  extent  of  11.1  per  cent  in  all  water  but  it  is  an 
essential  constitutent  of  organic  matter,  such,  as  cellulose.  It  is 
the  essential  constituent  of  all  acids  and  is  present  in  important 
amounts  in  all  hydrocarbons,  from  the  simplest  compounds  pres- 
ent in  natural  gas  to  the  most  complex  in  heavy  oils,  waxes  and 
coal. 

Since,  in  respect  to  availability,  water  far  transcends  the  hy- 
drocarbon family,  it  is  natural  that  the  main  source  of  indus- 
trial hydrogen  is,  in  the  last  analysis,  water.  In  certain  cases, 
the  production  of  the  gas  is  attained  with  the  utilisation  of  coal, 
coke  or  carbon  in  one  or  other  form,  as  an  auxiliary.  The  carbon, 
however,  functions  essentially  as  the  reducing  agent  employed  to 
liberate  the  element  from  the  compound  with  oxygen.  Physical 
methods  of  disruption  of  the  compound  may  also  be  used.  Thus, 

1  Day  and  Shepherd,  Bull.  Geo.  Soc.  America,  1913,  24. 


INTRODUCTION  19 

electrolysis  of  aqueous  solutions  of  acids  or  alkalis  has  an  impor- 
tant place  in  hydrogen  technology.  From  hydrocarbons,  the  hy- 
drogen may  be  obtained  by  processes  of  thermal  decomposition, 
in  contrast  to  the  case  of  water,  where  thermal  decomposition  is 
technically  impossible  owing  to  the  high  temperatures  which 
would  necessarily  be  involved.  Indirect  methods  of  obtaining 
hydrogen  from  hydrocarbons  requiring  chemical  interaction  either 
with  steam  or  carbon  dioxide  have  been  suggested,  but  they  have 
not  attained  to  practical  importance.  As  will  be  seen,  also, 
hydrogen  is  obtained  as  a  by-product  and  in  small  amounts 
from  other  classes  of  compounds  such  as  formates,  alcohols  and 
acetone. 

Classification  of  the  Systems  of  Hydrogen  Production. — The 
broadest  system  of  classification  will  naturally  be  based  on  the 
source  of  the  hydrogen,  whether  from  water,  hydrocarbon,  or 
other  source.  The  multiplicity  of  methods  of  obtaining  the  gas 
from  water  demands,  however,  a  more  elaborate  system  of  sub- 
division of  this  section.  This  can  conveniently  be  accomplished 
by  relegating  to  distinct  chapters  the  treatment  of  the  methods 
of  hydrogen  production  in  which  different  forms  of  the  raw  ma- 
terial are  concerned.  Thus,  water  comes  into  use  for  hydrogen 
manufacture  as  steam  and  as  water  as  well  as  in  the  form  of 
the  derived  raw  material,  water  gas.  In  the  succeeding  classifi- 
cation an  attempt  has  been  made  at  an  orderly  arrangement  of 
the  many  processes  to  be  considered,  with  this  idea  as  the  guid- 
ing principle.  The  order  of  raw  materials  has  been  chosen 
with  the  purpose  of  bringing  forward  first  for  consideration  the 
methods  of  manufacture  which  are  at  present  of  major  impor- 
tance. Thus  arranged,  the  groups  and  sub-groups  come  up  for 
treatment  as  follows: 

A.    Hydrogen  from  Water: 

I.    From  Steam 

(1)     By     alternate 


interaction   of 
iron     with  - 
steam  and  of 
iron  oxide 
with  water  gas 


(a)  Multi-retort  processes 

(b)  Single  retort  processes 


20 


INDUSTRIAL  HYDROGEN 


II.    From  Steam  and  Wa- 
ter Gas 


(1) 


By  continuous 
interaction  in 
presence  of  a 
catalyst 


(a)  The  Continuous  or  Ba- 
dische  Process 

(b)  Processes  with   displace- 
ment   of    equilibrium. 
Grieshei'm-Elektron  Co.'s 
process 

(c)  Single  stage   or  Dieffen- 
bach   and  Moldenhauer 
process 


III.    From  Water  Gas 


(1) 


By  processes 
of  liquefac- 
tion, involving 
carbon  mon- 
oxide  re- 
moval 


(a)  Linde-Frank-Caro    proc- 
ess 

(b)  Claude  process 


IV.    From  Water 


(1)  By  electrolysis.    Various  plant  types 

(2)  Employing  carbon  or  iron  and  water  under  pres- 
sure.   Bergius  process 

(3)  Employing  alkali  metals 

(4)  Employing  hydrides 

(5)  Employing  metallic  alloys 


V.    From  Aqueous  Alkalis  and  Hydroxides 

4 

(1)     Employingf(a)     The  Ferro_smcon  process 
(b)     Aluminium  process 


metals 
loys 


or  al-  -I 


B.    Hydrogen  from  Hydrocarbons: 

(1)  By  thermal  decomposition 

(2)  By  interaction  with  steam 

(3)  By  interaction  with  carbon  dioxide 


INTRODUCTION  21 

C.    Hydrogen  from  Miscellaneous  Sources  including  By-product 
Hydrogen: 

(1)  By  decomposition  of  formates 

(2)  By  dehydrogenation  of  alcohol 

(3)  By  fermentation  processes  to  yield  acetone 

(4)  The  Hydrogenite  process 

(5)  Hydrogen  from  sulphides 

(6)  Hydrogen  from  acids. 

The  processes  included  in  A  I,  A  II,  A  III  and  A  IV  (1)  form 
the  subject  matter  of  Chapters  II  to  V  inclusive.  Chapter  VI 
deals  with  the  chemical  methods  of  obtaining  hydrogen  from  wa- 
ter. The  succeeding  chapter  is  devoted  to  hydrogen  from  aqueous 
alkalis  and  hydroxides.  Chapter  VIII  sketches  out  the  prob- 
lems listed  under  B,  hydrocarbons  forming  the  raw  material. 
Chapter  IX  collects  the  miscellaneous  methods  of  manufacture 
and  discusses  by-product  hydrogen.  A  final  chapter  is  added  on 
the  purification  and  testing  of  hydrogen. 

Choice  of  Processes. — In  the  succeeding  chapters  it  will 
emerge  that  a  variety  of  processes  have  attained  to  a  standardised 
technical  development.  Enquiry  will  therefore  naturally  be 
forthcoming  as  to  preferred  processes  among  so  many.  The  an- 
swer to  such  enquiry  can  only  be  intelligently  given  with  refer- 
ence to  the  particular  usage  to  which  the  product  is  to  be  put  and 
also  with  reference  to  the  locality  in  which  the  gas  is  to  be  pro- 
duced. For  operations  involving  small  consumptions  of  gas,  say 
a  few  hundred  feet  of  gas  per  hour,  it  is  probable  that  an  elec- 
trolytic unit  would  best  meet  the  case.  The  relatively  high  in- 
itial outlay  and  cost  of  power  required  would  be  offset  by  the 
minimum  attention  needed  by  the  plant.  For  large  consumption 
the  cost  of  plant  and  cost  of  production  become  paramount.  For 
example,  in  the  synthesis  of  ammonia,  where  the  hydrogen  repre- 
sents as  much  as  75  per  cent  of  the  gas  mixture  employed  and 
about  17.5  per  cent  of  the  weight  of  ammonia  produced,  these 
considerations  outweigh  all  others  and  recourse  is  had  to  that 
process,  the  catalytic  process  (Chapter  III),  in  which  the  hydro- 
gen can  be  most  cheaply  produced.  The  presence  of  nitrogen  as 
an  almost  inevitable  impurity  in  such  gas,  however,  limits  its 
applicability  in  other  directions  than  that  of  ammonia  synthesis, 
in  which  process,  of  course,  the  nitrogen  is  a  needed  constituent 


22  INDUSTRIAL  HYDROGEN 

of  the  gas  mixture.  Hence  we  find  that,  in  the  field  of  aeronautics 
and  in  the  hydrogenation  of  oils,  more  expensive  but  purer  grades 
of  hydrogen  are  in  use,  for  example,  steam-iron  process  and  elec- 
trolytic hydrogen  in  the  majority  of  cases. 

Since,  in  the  electrolytic  process  both  hydrogen  and  oxygen 
are  produced,  the  localisation  of  the  plant  is  an  important  factor 
in  the  determination  of  the  process  to  be  preferred.  In  several 
cases  in  this  country  the  substitution  of  electrolytic  hydrogen 
for  other  processes  has  resulted  in  considerable  economic  benefit 
owing  to  the  revenues  accruing  from  the  disposal  of  the  by- 
product oxygen.  Similar  returns  from  oxygen  disposal  are  pos- 
sible in  the  case  of  the  Linde  process  of  hydrogen  production 
from  water  gas  (Chapter  IV)  in  which,  by  rectification  of  the 
liquid  air  used  in  the  liquefaction  process,  oxygen  and  nitrogen 
may  be  received  as  by-products.  In  the  early  stages  of  de- 
velopment of  the  synthetic  ammonia  process  at  Oppau,  Ger- 
many, the  nitrogen  required  was  so  obtained,  the  saving  thus 
accruing  being  credited  to  the  hydrogen  process. 

Attention  should  be  directed  to  the  desirability,  in  certain  cir- 
cumstances, of  combining  two  types  of  unit.  For  steady  produc- 
tion the  unit  chosen  should  provide  hydrogen  of  the  necessary 
grade  at  a  minimum  cost  inclusive  of  investment  cost.  For  emer- 
gency purposes,  as  for  example,  during  overhaul  periods  or  when 
an  excess  of  gas  is  required  for  a  special  occasion,  the  pro- 
vision of  a  stand-by  unit,  low  in  investment  cost,  is  desirable. 
A  unit  of  the  silicol  process  type  (Chapter  VII)  fulfills  such  a 
purpose  and  should  be  of  special  importance  in  aeronautic  work 
where  great  demands  often  occur,  as  in  the  first  inflation  of  a 
ship,  or  after  a  gas  bag  has  been  ripped  in  a  big  ship,  or  when 
the  entire  gas  contents  must  be  changed  in  a  smaller  vessel. 

Safety  Precautions. — Especial  care  is  necessary  in  the  opera- 
tion of  hydrogen  production  owing  to  the  dangers  of  fire  and  ex- 
plosion associated  with  the  gas  and  the  gaseous  materials  with  the 
aid  of  which  it  may  be  produced.  The  ignition  point  of  hydro- 
gen gas  is  low,  circa  580-590°  C.,  dependent,  however,  to  some 
extent  on  the  concentration  of  the  gas  and  the  oxygen-nitrogen 
ratios.4  Carbon  monoxide,  which  is  the  other  principal  combus- 

«K.  G.  Falk,  J.  Amer.  Chem.  8oc.f  1907,  92,  1536.  Dixon  and  Coward, 
J.  Chem.  Soc.f  1909,  95,  514. 


INTRODUCTION  23 

tible  constituent  in  the  water-gas  from  which  hydrogen  is  fre- 
quently obtained,  has  an  ignition-point,  according  to  the  same 
authors,  varying  between  637  and  658°  C.  in  oxygen,  and  be- 
tween 644°  and  658°  C.  in  air. 

Combustion  of  inflammable  gases  mixed  with  air  or  oxygen 
will  only  take  place  within  fairly  well  defined  limits  of  concen- 
tration. To  ensure  propagation  of  flame,  it  is  necessary  (1)  that 
the  initial  source  of  heat  should  be  of  a  volume,  intensity  and 
duration  sufficient  to  raise  the  layer  of  gases  in  its  immediate 
vicinity  to  a  temperature  higher  than,  or  as  high  as,  the  ignition 
temperature  of  the  mixture;  and  (2)  that  the  heat  contained  in 
the  products  of  combustion  of  this  first  layer  should  be  sufficient 
to  raise  the  adjacent  layer  to  its  ignition  temperature.5  There 
are  two  limits  of  concentration,  the  one  is  the  lower  limit  of  in- 
flammation corresponding  to  the  smallest  concentration  of  com- 
bustible gas  which,  with  air  or  oxygen  will  enable  self-propaga- 
tion to  take  place.  The  other  or  upper  limit  corresponds  to  the 
maximum  concentration  which  will  so  act.  The  limits  vary  some- 
what with  the  shape  and  size  of  the  containing  vessel.  They  are 
extended  in  wider  vessels.  Increased  pressure  also  tends  to  widen 
the  limits,  as  does,  also,  increase  of  temperature.6  This  may, 
however,  be  specific  to  certain  gases,  since  Terres  and  Plenz7 
state  that  increase  of  pressure  narrows  the  limits  in  the  case  of 
carbon  monoxide-air  and  hydrogen-air  mixtures.  The  data  for 
the  several  gases  concerned,  as  compiled  from  recent  data,  are 
given  in  the  following  tables,  referring  to  explosive  limits  at 
atmospheric  pressure  with  gas-air  mixtures: 


Gas 

Lower  Limit 

Upper  Limit 

Hydrogen  8  

4.1 

74.2 

Carbon  monoxide  8  .  . 
Methane  8  

12.5 
53 

74.2 
15.4 

Water-gas  9  

124 

66.8 

5  Burgess  and  Wheeler,  J.  Chem.  Soc.,  1911,  99,  2,013. 

•  See  Burrell  and  Ganger,  Bur.  of  Mines,  Tech.  Paper,  No.  150.  Burrell 
and  Robertson,  Bur.  of  Mines,  Tech.  Paper,  No.  121. 

7J.  Gasbeleucht.,  1914,  57,  990,  1,001,  1,016. 

8  Coward,  J.  Cliem.  Soc.t  1914,  105,  1,859.  Coward,  Carpenter  and  Pay- 
man,  /bid.  1919,  115,  27. 

•Bunte,  1901. 


24  INDUSTRIAL  HYDROGEN 

Since  the  sensitivity  of  hydrogen  to  explosion  is  so  great,  the 
greatest  care  is  essential  in  exposing  hydrogen  streams  to  flames. 
Certainty  is  indispensable  in  this  connection.  As  a  consequence, 
adequate  "purging"  of  a  system,  with  hydrogen  known  to  be  safe 
as  regards  oxygen  content,  should  always  be  carried  through 
before  flames  are  brought  into  action.  Absence  of  oxygen  is  to 
be  strongly  recommended  when  inflammable  gases  are  under- 
going compression,  since  the  momentary  rise  of  temperature  of 
the  gas  during  the  compression  stroke  may  be  sufficient  to  bring 
about  explosion.  Furthermore,  in  the  release  of  compressed  hy- 
drogen to  closed  systems,  as,  for  example,  to  gauges,  the  opera- 
tion should  always  be  performed  gradually,  since  sudden  open- 
ing of  the  valve  may  cause  adiabatic  compression  of  the  first 
gas  and  of  air  or  oxygen  in  the  gauge,  with  consequent  rise  in 
temperature. 


Chapter  II. 
Hydrogen  From  Steam. 

The  great  bulk  of  hydrogen  consumed  in  the  hydrogenation 
of  oils  is  produced  by  means  of  the  steam-iron  process.  The  hy- 
drogen is  generated  by  the  interaction  of  steam  with  iron  at  tem- 
peratures ranging  according  to  choice  from  550°  C.  to  800°  C. 
The  reaction,  which  may  be  formulated  by  means  of  the  equation, 

3Fe  +  4H20  =  Fe304  +  4H2 

is  in  reality  a  reversible  process.  Low  temperatures  favor  hydro- 
gen production,  high  temperatures  the  reduction  of  iron  oxide. 
Furthermore,  the  total  reaction  may  be  regarded  as  occurring  in 
two  stages, 

(a)  3Fe    +  3H20  =  3FeO  +  3H2 

(b)  3FeO+   H20  =  Fe304+   H2 

and  in  each  stage  definite  equilibrium  relationships  hold.  The 
data  of  Chaudron x  plotted  in  the  accompanying  diagram,  Fig.  I, 
show  the  respective  ratios  of  pjj  Q/PH  *or  vari°us  temperatures 
when  the  solid  phases  present  are  Fe-FeO  and  FeO-Fe304  re- 
spectively. It  will  be  seen  that,  in  the  region  of  operating  tem- 
peratures chosen,  both  oxidation  and  reduction  may  take  place  to 
a  marked  degree  according  to  the  nature  of  the  contact  material 
and  the  gas  passing  over  it.  Thus,  if  the  contact  mass  be  iron  or 
ferrous  oxide,  treatment  with  steam  will  result  in  hydrogen  pro- 
duction. If  the  mass  be  magnetic  oxide  of  iron,  Fe304,  and  the 
gas  passing  be  hydrogen,  marked  reduction  will  occur.  The 
steam-iron  process  is  operated  with  such  an  alternation  of  re- 
actions. Hydrogen  is  produced  by  passage  of  the  steam  over  the 
reduced  contact  mass,  the  magnetic  oxide  of  iron  thereby  pro- 
duced being  reduced  in  a  succeeding  operation  to  the  metallic 

^omptes  rend.,  1914,  159,  237.  See,  however,  Schreiner  and  Grimnes, 
Zeit.  anorg.  Chem.,  1920,  110,  311,  who  obtain  somewhat  different  values,  which, 
however,  are  no  more  satisfactory  when  correlated  with  the  equilibrium  data 
using  carbon  monoxide  nor  with  the  equilibrium  in  the  water-gas  reaction.  See 
also  Appendix  I. 

25 


26 


INDUSTRIAL  HYDROGEN 


or  lower  state  of  oxidation  by  means  of  a  suitable  reducing  gas. 
For  technical  purposes,  the  reducing  gas  most  generally  em- 
ployed is  water-gas,  being  the  gas  with  the  maximum  content  of 
reducing  agents  consistent  with  the  economy  of  the  process. 


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FIG.  I.     Fe-FeO  and  FeO-Fe3O4  Equilibria. 

Hence,  the  reduction  of  the  contact  mass  involves  two  reactions, 
the  first  being  the  reverse  of  that  occurring  in  the  steaming  phase 

Fe304  +  4H2  =  3Fe  +  4H20 
which  really  occurs  in  two  stages 

Fe304+    H2  =  3FeO+   H20 
3FeO  +  3H2  =  3Fe    +  3H20, 

the  second  being  the  corresponding  reaction  with  carbon  mon- 
oxide— a  reaction  which  also  may  be  formulated  in  two  stages 

Fe304+   CO  =  3FeO+   C02 
3FeO  +  3CO  =  3Fe    +  3C02. 

As  with  the  corresponding  reaction  involving  steam  and  hydro- 
gen, these  reactions  are  also  reversible  and  the  equilibrium  ratios 


HYDROGEN  FROM  STEAM 


27 


of  the  carbon  dioxide  and  carbon  monoxide  at  various  tempera- 
tures are  set  forth  graphically  in  the  accompanying  diagram,  Fig. 
II,  compiled  from  the  best  available  data  on  the  equilibria.2 
Other  reducing  gases,  such  as  producer  gas,  may  be  employed,  as 
will  be  indicated  later.  In  principle,  however,  the  process  and  the 
reactions  occurring  are  not  affected  by  such  change. 

Historical. — The  essential  reaction,  the  interaction  of  steam 
and  iron  is  a  very  old  one  and  was  early  embodied  in  patent  ap- 
plications. Joseph  Jacob  (B.  P.  593/1861)  claimed  the  commer- 
cial production  of  hydrogen  by  the  action  of  steam  on  iron  bor- 


O^ 

k 

GOO 
700 

eoo 
zoo 

.0 

k 

aoo 

7OO 

eoo 

soo 

300 

^ 

V 

\N 

s\ 

^x 

JJ 
0^) 

xft 

m 

, 

^< 

)^-- 

" 

/^. 

Q+ 

"  fl 

>o 

6O 


^x 

s 

S* 

,'' 

' 

5* 

?^ 

T  •' 

'-' 

/^ 

b- 

/^ 

•*0         SO        GO         7O 

'/•CO 

30        -4O         SO 

xco 

FIG.  II.     Fe-FeO  and  FeO-Fe3O4  Equilibria. 

ings  or  filings  or  on  iron  crushed,  ground  or  pulverised.  A  por- 
tion of  the  hydrogen  produced  was  to  be  burned  on  the  outside  of 
the  retorts  in  order  to  maintain  the  reaction  temperature.  The 
iron  after  interaction  with  the  steam  was  to  be  discharged  from 
the  retorts  and  utilised  for  other  purposes.  Similar  early  patent 
claims  are  due  to  Isham  Baggs  (B.  P.  2,719/1865  and  1,471/ 
1873).  An  unsuccessful  attempt  at  commercial  production  by 
the  steam-iron  process  was  made  by  Giffard  in  1878.  The  iron 
rapidly  became  inactive  due  to  sintering  of  the  material  and 
to  chemical  reaction  with  impurities  in  the  reducing  gases  used. 
The  Lewes  patents,  B.  P.  20,752/1890  and  4,134/1891,  repre- 
sent the  beginnings  of  a  serious  attempt  to  solve  the  commercial 

2Schenck,  Ber.  1905,  38,  2,132;  1907,  W,  1,708.  van  Royen.  Disa.  Bonn. 
1911.  Levin  and  Koster.  Nernst  Festcfirift.  Falcke.  Z.  Elektrochem,  1916, 
22,  121. 


28  INDUSTRIAL  HYDROGEN 

production  of  pure  hydrogen.  In  the  earlier  claim,  the  contact 
mass,  iron  turnings  or.  a  suitably  moulded  oxide,  was  to  be  con- 
tained in  a  retort  embedded  in  the  fuel  bed  of  a  gas  producer 
making  an  air  producer  gas.  Thereby,  the  mass  was  to  be  main- 
tained at  a  sufficient  temperature  and  the  producer  gas  was  to 
be  used  for  the  reducing  phase.  In  the  later  claim,  various  forms 
of  contact  mass  are  mentioned,  including  iron  obtained  from  its 
salts  deposited  on  asbestos  or  pumice  or  obtained  by  admixture 
of  moist  hydroxide  of  iron  with  a  suitable  support  material.  A 
semi-water-gas  containing  both  carbon  monoxide  and  hydrogen  in 
addition  to  nitrogen  is  also  cited  as  preferable  to  carbon  mon- 
oxide and  nitrogen  alone. 

Development  of  the  engineering  details  associated  with  the 
proposals  of  Lewes  relative  to  hydrogen  production  was  energeti- 
cally undertaken  in  England  by  Lane.  The  resulting  improve- 
ments are  embodied  in  several  patents  to  Lane  and  others.3  They 
resulted  in  a  departure  from  the  single  shaft  of  material  as  pro- 
posed by  Lewes  and  the  substitution  of  a  multi-retort  plant  which 
has  been  largely  employed  in  the  Lane  form  or  with  modifications 
introduced  by  other  plant  erectors.  Details  of  such  plant  will 
be  considered  later. 

The  single  retort  unit,  on  the  other  hand,  has  been  intensively 
studied  and  developed  by  German  investigators.  The  principal 
plant  based  on  this  system  is  the  Messerschmitt  plant  of  which 
several  modifications  exist.4  Modifications  of  the  single  retort 
unit  are  also  due  to  the  Badische  Anilin  u.  Soda  Fabrik  and 
others. 

The  Contact  Mass. — Since  the  reaction  with  steam  occurs 
mainly  on  the  surface  of  the  iron  and  penetrates  little,  if  any, 
into  the  interior  of  the  solid  mass,  it  is  desirable  that  the  iron  em- 
ployed should  be  in  such  a  form  as  to  expose  the  maximum 
amount  of  surface  consistent  with  the  other  properties  requisite 
in  the  chosen  material.  A  porous  reactive  form  of  iron  is  there- 
fore chosen.  On  the  other  hand,  the  contact  mass  should  be 
physically  robust,  as  the  alternation  of  oxidation  and  reduction 
promotes  disintegration,  leading  to  accumulation  of  finer  ma- 

»  Hills  and  Lane  B.  P.  10,356/1903.  Lane  and  Monteux  Fr.  P.  386,991/1908. 
Lane,  B.  P.  17,591/1909 ;  11,878/1910.  U.  S.  P.  1,028,366/1912.  1,040,218/1912 ; 
1,078,686/1913. 

*  D.  R.  P.  291,902/1914  ;  U.  S.  P.  1,109,447/1914  ;  U.  S.  P.  1,152,196/1915  ; 
U.  S.  P.  1,225,262/1917  ;  U.  S.  P.  1,225,263/1917 ;  U.  S.  P.  1,225,264/1917. 


HYDROGEN  FROM  STEAM  29 

terial  and  the  development  of  a  back-pressure  in  the  retort- 
system.  Difficulties  arise  also  in  choice  of  contact  material  owing 
to  the  tendency  towards  local  overheating  within  the  retorts, 
which  results  in  a  sintering  of  the  mass,  loss  of  activity  and 
consequent  diminution  of  hydrogen  yield. 

Material  of  suitable  quality  is  generally  obtained  from  a  car- 
bonaceous or  oxide  ore  of  iron  which,  after  calcination  and  re- 
duction, is  in  the  requisite  porous  condition.  The  material  most 
commonly  employed  is  a  calcined  spathic  iron  ore.  Originally  a 
carbonate  of  iron,  the  ore  suffers  loss  of  carbon  dioxide  on  heat- 
ing and  yields  an  oxide  of  the  requisite  quality.  A  certain  amount 
of  fusion  occurs  in  the  calcination  process.  The  material  has 
somewhat  the  porous  appearance  of  coke  but  is  considerably 
denser,  very  robust  and  resistant  to  disintegration.  Claim  is 
made  for  such  a  contact  mass  in  the  patent  of  Dieffenbach  and 
Moldenhauer.5  It  was,  however,  employed  in  technical  practice 
some  years  previous  to  the  date  of  this  application.  Before  1917, 
American  producers  of  hydrogen  by  the  steam-iron  process  im- 
ported their  contact  material,  mainly  from  England.  During 
the  war  it  was  necessary  to  make  use  of  home  supplies  of  iron 
ores  but  these  were  found  to  be  much  inferior  to  the  imported 
calcined  spathic  ore.  In  addition  to  the  English  product  a  con- 
tact mass  obtained  by  calcination  of  a  Spanish  carbonaceous  iron 
ore  has  been  used  with  success. 

The  nature  of  one  method  of  preparation  is  disclosed  in  a 
patent  to  Bates  and  Bates  (B.  P.  134,155/1919)  according  to 
which  the  material  is  obtained  in  suitable  form  for  use  by  stack- 
ing the  spathic  ore  in  heaps  with  a  covering  of  small  fuel,  allowing 
the  heap  to  burn  slowly  for  several  days.  The  hot  heap  is  then 
quenched  with  water  and  the  ore  when  cold  is  washed  with  water 
to  free  it  from  impurities.  The  British  Oxygen  Co.,  Bray  and 
Balfour,  soak  the  ore  for  one-half  hour  in  commercial  hydro- 
chloric acid,  after  which  it  is  washed  thoroughly  with  water  and 
is  dried  for  use.  A  more  porous  and  active  material  is  thereby 
produced  (B.  P.  122,474/1918),  it  is  claimed. 

The  Dellwik-Fleischer  Co.  claim6  the  use  of  burnt  pyrites 
as  contact  material.  When  roasted  to  expel  all  the  sulphur  the 
material  is  not  generally  very  reactive,  and,  if  the  calcination  is 

"D.  R.  P.  232,  347/1910. 
•B.  P.  7,849/1909. 


30  INDUSTRIAL  HYDROGEN 

stopped  short  of  complete  removal  of  sulphur,  the  hydrogen  in- 
itially produced  contains  a  high  concentration  of  sulphur  com- 
pounds. With  use,  however,  the  material  improves. 

A  high  grade  contact  mass  is  obtainable  from  Swedish  iron 
ore,  an  oxide  ore  of  exceptional  purity,  low  in  sulphur  and  phos- 
phorus. The  oxide  may  be  utilised  directly  for  charging  into  the 
retorts,  where,  after  reduction,  it  possesses  the  requisite  porous 
condition  and  strength.  An  improved  form  of  this  material  is 
obtained  by  admixture  of  the  broken  ore  with  limestone  and 
carbon  in  suitable  form.  The  material  is  then  calcined  at  rela- 
tively low  temperatures,  reduction  of  the  oxide  being  effected  by 
the  carbon  monoxide  produced  in  the  combustion  process.  In 
this  way  a  spongy  form  of  iron  of  high  reactivity  and  consider- 
able strength  may  be  obtained.  It  is,  however,  relatively  costly. 
Such  material  also  forms  a  suitable  basis  for  contact  material 
in  the  water  gas  catalytic  process  discussed  elsewhere. 

In  addition  to  reduced  iron  ores,  other  contact  agents  have 
been  employed.  Alloys  of  iron,  especially  with  manganese,  chro- 
mium, tungsten  and  titanium  are  claimed  in  the  patent  of  Dieffen- 
bach  and  Moldenhauer.7  Ferro-manganese  shows  a  higher  rate 
of  reactivity  with  steam  than  does  a  compact  iron  under  similar 
conditions.  During  the  war,  patents  employing  such  alloys  were 
utilised  by  English  hydrogen  producers  under  license,  in  place  of 
iron  ore  contact  masses.  Such  alloys  show  less  tendency  to  sinter 
with  local  overheating  and  thus  lose  their  activity  less  rapidly. 
They  also  deteriorate  less  with  use.  According  to  Messer- 
schmitt,8  manganese  additions  are  of  especial  value  in  prevent- 
ing carbon  deposition  in  the  contact  mass,  a  circumstance  tend- 
ing, as  will  be  shown,  towards  a  purer  hydrogen  product.  Such 
contact  agents,  however,  obviously  entail  a  high  outlay  for  con- 
tact material. 

Impregnation  of  spongy  Swedish  iron  with  an  alkali  hydrate 
or  carbonate  is  a  modification  of  the  contact  mass  employed  by 
Thorsell  and  Lunden  in  Sweden  to  increase  the  active  life  of 
the  contact  mass.9  Iron  thus  treated  is  probably  much  more 
reactive  towards  steam  than  the  untreated  material.  It  should 
therefore  be  possible  to  operate  at  lower  reaction  temperatures 

7  B.  P.  12,051/1912. 

8U.   S.   P.   1,109,448/1914. 

•  See  B.  P.  119,591/1918. 


HYDROGEN  FROM  STEAM  31 

and  thus  diminish  loss  of  activity  due  to  sintering.  Examination 
of  active  material  and  the  same  material  after  use  and  consequent 
loss  of  activity,  shows,  in  the  former  case,  an  open  porous  struc- 
ture and,  in  the  latter,  a  smoother  surface  due  both  to  loss  by 
abrasion  and  to  local  fusion  of  the  surface.  Lower  reaction  tem- 
peratures therefore  favour  increased  duration  of  active  life  of  the 
contact  mass.  Similar  claims  to  those  of  Lunden  and  Thorsell 
have  been  made  by  Maxted,10  who  recommends  addition'  of  al- 
kalis, alkaline  earths  and  copper  salts. 

The  Badische  Anilin  u.  Soda  Fabrik11  patented  the  use  of 
oxide  of  iron  prepared  synthetically  by  fusion  of  iron  in  oxygen. 
Incorporation  of  refractory  oxides  such  as  magnesia  or  zirconia 
in  such  synthetically  prepared  materials  was  also  suggested. 
There  is  no  evidence  that  such  synthetic  contact  masses  have 
come  into  general  use  and,  it  is  evident,  they  must  have  a  high 
initial  cost  compared  with  oxides  of  iron  produced  from  natural 
iron  ores. 

Typical  Generator  Units — (a)  Multi-retort  type. — The  pio- 
neer hydrogen  generator  of  the  multi-retort  type  is  that  due  to 
Lane  and  examples  of  this  system  of  operation  are  to  be  found 
in  America,  England,  France  and  Russia  in  the  factories  which 
were  among  the  earliest  to  concern  themselves  with  the  hydro- 
genation  of  oils. 

A  Lane  generator  unit  contains  three  sets  of  twelve  retorts 
each  filled  with  the  material  used  as  contact  mass.  The  retorts 
are  arranged  vertically  in  a  rectangular  firebrick  combustion 
chamber  in  groups  as  indicated  in  the  diagram  (Fig.  III).  They 
average  10  to  12  feet  in  length  with  an  internal  diameter  of  9 
inches.  They  are  closed  at  the  two  ends  by  means  of  plates 
bolted  to  flanges  on  the  retort  ends,  asbestos  joints  being  used 
to  make  the  fittings  gas-tight.  With  suitable  valve  and  pipe  con- 
nections, diagrammatically  shown  in  Fig.  IV,  the  sets  may  be 
supplied  with  water-gas  or  steam,  the  direction  of  these  gas 
streams  being  opposite  to  one  another  through  the  retorts.  Lane 
found 12  that  the  reducing  stage  was  considerably  less  rapid  than 
the  steaming  phase.  Consequently,  the  generator  is  so  arranged 
that  two  of  the  three  sets  of  12  retorts  are  being  treated  with 

10  B.  P.  125,410/1916. 

11  B.  P.  6,683/1912. 
13  B.  P.  17,591/1909. 


32  INDUSTRIAL  HYDROGEN 

water-gas  while  the  third  set  is  being  steamed.  With  a  steam- 
ing phase  of  10  minutes'  duration  the  time  occupied  in  the  reduc- 
tion is  therefore  20  minutes  and  a  cycle  is  established  whereby 
hydrogen  is  generated  from  the  three  sets  in  succession  once  every 
half  hour.  With  this  arrangement  as  to  time  and  with  a  unit  of 


Front       Elevation 

FIG.  III.     (a)  Front  Elevation  of  Lane  Generator  Unit.     (The  Engineer.) 

the  size  stated,  an  hourly  production  of  3,500  cubic  feet  of  hy- 
drogen is  possible.  After  the  reducing  period,  the  retorts  are  full 
of  partially  spent  water-gas.  To  avoid  introduction  of  this  gas 
into  the  hydrogen  obtained  when  the  steam  is  turned  into  the  re- 
tort system  Lane  introduced  a  brief  period  of  "scavenging"  or 
"purging"  between  the  reducing  phase  and  the  hydrogen  make. 
For  15  to  30  seconds  after  the  steam  is  admitted,  the  hydrogen 


HYDROGEN  FROM  STEAM 


33 


34 


INDUSTRIAL  HYDROGEN 


produced  is  allowed  to  follow  the  spent  water-gas  until  the  retort 
system  is  sufficiently  freed  from  carbon-containing  gases.  Then, 
by  a  change-over  valve,  it  is  diverted  to  the  hydrogen  purification 
system  and  holder. 

To  maintain  the  reaction  temperature,  the  spent  water-gas, 
which  still  contains,  after  leaving  the  retort  system,  a  marked 
proportion  of  combustible  gases,  is  cooled  in  a  scrubber  condenser 
to  free  it  from  steam  and  is  then  returned  to  the  generator  to  be 


Ovt/et 


FIG.  IV.     Diagrammatic  Representation  of  Valve  System 

burned  on  the  outsides  of  the  retorts.  The  gas  is  led  in  pipes 
through  holes  in  the  lower  section  of  the  combustion  chamber  and 
burned  around  the  base  of  the  outside  retorts  of  the  setting.  A 
simple  length  of  iron  pipe  serves  as  burner  since  the  gas  requires 
no  admixture  with  air  prior  to  combustion. 

Several  modifications  of  the  Lane  plant  have  been  made  in 
later  forms  of  the  multi-retort  generator.  Thus,  a  number  of 
plants  recently  erected  provide  a  producer  along  with  the  re- 
tort setting  and  placed  about  six  feet  below  the  same.  The  pro- 
ducer delivers  to  the  outside  of  the  retorts  a  producer  gas  through 


HYDROGEN  FROM  STEAM  35 

flues  arranged  between  the  two  parallel  sets  of  retorts.  Secondary 
air,  preheated  by  passage  through  the  combustion  chamber,  is 
utilised  for  combustion  of  the  producer  gas.  The  products  of 
combustion  may  or  may  not  pass  through  heat  recovery  units. 
With  such  a  method  of  heating,  it  is  claimed,  a  more  even  tem- 
perature can  be  obtained  than  is  possible  with  generators  burn- 
ing spent  water-gas.  One  such  unit  showed  a  working  tempera- 
ture of  625°  C.  with  a  normal  variation  of  ±  5°  C.  On  the 
other  hand,  the  available  heat  units  of  the  spent  water-gas,  which, 
as  shown  in  the  Lane  practice  are  adequate  for  temperature  main- 
tenance, will  not  be  utilised  unless  special  uses  are  found  for  such. 
In  one  plant  the  spent  water-gas  is  utilised  in  raising  steam  for 
the  steaming  phase.  According  to  Ballingall 13  the  spent  water- 
gas  leaving  the  retorts  may  be  raised  in  temperature  in  a  heat 
interchanger,  and  led  through  the  reaction  zone  of  a  gas  pro- 
ducer. Here  the  carbon  dioxide  and  steam  are  partially  reduced 
to  combustible  gases,  which  are  then  burned  with  an  insufficient 
amount  of  air  around  the  retorts.  A  further  addition  of  air 
then  permits  the  completion  of  the  combustion  process  and  the 
hot  gases  are  used  in  the  heat  interchanger  to  preheat  the  gases 
leaving  the  retort  system.  It  is  obvious  that,  in  this  mode  of 
procedure,  the  fuel  consumption  is  greater  than  in  the  simple 
Lane  procedure  although  possibly  not  so  great  as  in  the  case 
where  heating  is  effected  by  means  of  producer  gas  alone.  In  this 
latter  case,  a  coke  consumption  of  30  cwt.  per  100,000  cubic  feet 
of  hydrogen  produced  per  day,  in  addition  to  that  consumed  in 
making  the  reducing  gas,  is  representative  of  average  practice. 

A  modification  of  the  Lane  system  applicable  where  a  large 
hydrogen  output  is  required,  consists  in  employing  three  generator 
units  each  of  36  retorts  for  the  reduction-oxidation  cycle  instead 
of  dividing  each  unit  into  three  sets  of  twelve  retorts.  In  this 
case  one  whole  unit  is  producing  hydrogen  while  the  other  two 
units  are  being  reduced.  It  is  evident  that,  with  such  an  arrange- 
ment, an  economy  of  valves  and  piping  is  obtained,  since,  to  each 
unit  one  set  of  valves  in  place  of  the  three  shown  in  the  diagram 
(Fig.  Ilia)  are  sufficient.  In  another  modification,  in  use  in  this 
country,  the  setting  contains  but  12  retorts  which  are  larger  in 
dimensions  than  those  in  the  36  retort  units. 

As  will  be  discussed  in  detail  later,  carbon  and  some  sulphur 

MB.  P.  106,067/1917. 


36  INDUSTRIAL  HYDROGEN 

compounds  generally  accumulate  in  the  contact  mass.  These 
bodies,  which  give  rise  to  impurities  in  the  hydrogen  produced, 
are  periodically  removed  by  blowing  or  pulling  air  through  the 
retorts.  The  accumulations  are  thus  oxidised  to  carbon  mon- 
oxide, carbon  dioxide  and  sulphur  dioxide.  The  "burning-off" 
process  is  accomplished  either  by  compressed  air  from  a  blower 
or  by  means  of  a  steam-ejector  which  pulls  the  air  through  the 
retort  system.  The  "burning-off"  period  follows  upon  a  steaming 
phase  and  is  followed  by  the  usual  reduction  period  with  water- 
gas. 

The  life  of  the  retort  constitutes  a  factor  of  great  importance 
in  the  economy  of  the  multi-retort  process.  The  temperature 
maintained  and  the  attention  devoted  to  the  air-gas  ratio  used 
in  the  temperature  maintenance  largely  determine  the  length  of 
life  of  a  retort.  The  flame  employed  in  the  heating  process 
should  be  as  nearly  theoretical  for  complete  combustion  as  is 
practicable.  Excessive  oxidation  conditions,  especially,  cause  the 
retorts  to  scale  badly.  The  interior  of  the  retorts  do  not  suffer 
materially  in  the  cycle  of  operations.  With  a  working  tempera- 
ture of  about  650°  C.  an  average  retort  should  have  a  life  of 
12  months.  The  economy  of  alloys  and  alloy-steels  capable  of 
withstanding  high  temperatures  deserves  extended  study  by  the 
hydrogen  manufacturer. 

The  durability  of  the  ore  is  a  further  factor  of  economic  im- 
portance concerning  which  the  most  divergent  views  are  held. 
Average  practice  gives  the  ore  a  life  of  about  6  months,  so  that  a 
retort  of  average  life  will  be  charged  and  discharged  twice.  The 
usual  method  of  procedure  on  discharging  a  hydrogen  bench  is 
to  discard  entirely  those  retorts  in  poor  condition,  making  up 
the  new  furnace  with  a  series  of  retorts  either  all  new  or  all  of 
approximately  equal  state  of  repair.  After  discharging,  the  ore 
is  graded,  the  fine  material  being  rejected  and  that  of  suitable  size 
being  again  used  with  a  further  supply  of  new  ore.  On  the  other 
hand,  in  one  plant  known  to  the  writer,  a  much  more  frequent 
renewal  of  the  ore  is  usual  than  in  the  average  practice.  A  re- 
newal, on  an  average  once  every  two  months  is  effected  in  this 
case,  with  the  object  of  maintaining  a  high  reactivity  of  the  ma- 
terial and  consequent  high  output  of  hydrogen  from  a  single 
setting.  The  object  of  this  will  be  enlarged  upon  in  the  subse- 
quent discussion  on  the  ratio  of  water-gas  consumption  to  hydro- 


HYDROGEN  FROM  STEAM  37 

gen  produced.  It  is  held  in  this  case  that  the  extra  yield  thus 
obtained  more  than  balances  the  extra  cost  entailed  in  charging 
and  discharging  ore.  That  this  item  is  serious  is  evidenced  by  the 
devices  now  being  introduced  to  facilitate  the  operation.  Demp- 
ster 14  proposes  to  provide  the  retort  with  a  perforated  platform 
mounted  on  a  vertical  shaft  and  capable  of  being  raised  or  low- 
ered from  top  to  bottom  of  the  retort  in  the  filling  process.  Pro- 
jections on  the  internal  wall  of  the  retort  are  provided,  to  guide 
the  platform,  which  may  be  revolved  as  well  as  moved  vertically. 
A  more  recent  patent  claim 15  by  W.  J.  and  W.  R.  Bates,  calls 
for  the  use  of  perforated  or  open-work  cages  of  varying  mesh 
suitable  for  different  grades  of  ore.  The  coarsest  material  is  to 
be  placed  in  the  cages  at  the  bottom,  the  finest  at  the  top  of  the 
retorts.  Expanded  metal  is  used  for  the  bottom  and  body  of  the 
cage,  and  removable  lids  are  provided  to  close  the  top  during 
transport.  A  flange  or  projection  to  fit  the  top  of  the  cage  next 
beneath  it  in  the  retort  is  provided  for  each.  Eyes  are  fitted  for 
engagement  with  a  lifting  and  lowering  appliance  for  use  during 
charging  or  discharging. 

(b)  The  single  retort  type. — The  single  retort  represents  an 
attempt  to  avoid  some  of  the  difficulties  inherent  in  the  multi- 
retort  system  of  hydrogen  generation  by  the  steam-iron  process. 
Thus,  since  external  heating  involves  a  comparatively  small  nar- 
row retort,  the  unit  retort  system  employs  internal  heating  and 
a  large  contact  bed.  A  more  even  temperature  distribution  is  also 
sought  thereby.  The  choice  of  such  a  system  is  further  deter- 
mined by  considerations  of  wear  and  tear  in  the  multi-retort  sys- 
tem, and  also  of  difficulties  and  expense  involved  in  the  charging 
and  discharging  of  the  ore. 

This  type  of  generator  has  been  developed  principally  in 
Germany,  but  a  number  of  such  plants  have  been  recently  erected 
in  this  country  and  in  England. 

The  evolution  of  the  single-retort  unit  can  be  traced  through 
the  patent  specifications  of  Messerschmitt  already  cited.  The 
earlier  designs  called  for  cylindrical  beds  of  material.  Uneven 
temperature  distribution  apparently  resulted,  for  various  de- 
vices were  patented  to  avoid  fusion  of  the  contact  mass.  The 
mass  was  split  up  into  sections  by  plates,  grids  or  screens  of  iron, 

"B.  P.  104,115/1916. 
"  B.  P.  137,674/1919. 


38  INDUSTRIAL  HYDROGEN 

or  by  bars  of  iron  placed  vertically.  The  latest  modifications 
of  Messerschmitt 16  plant  substitute  for  a  cylindrical  bed  of  ma- 
terial a  narrow  annular  column  which  may  be  heated  by  a  cen- 
tral combustion  chamber  of  checker  brick  work,  or  may  be 
placed  between  two  checker  brick  columns.  In  this  later  type 
(compare  with  Figure  V  following)  water-gas  is  mixed  with  air 
insufficient  for  complete  combustion  and  introduced  into  the  cen- 
tral combustion  chamber.  The  mixture  there  reacts  and  the  hot 
reducing  gas  thus  produced  is  then  passed  downwards  through 
the  annulus  of  ore  to  bring  about  reduction  of  the  oxide  of  iron. 
It  is  then  mixed  with  a  further  quantity  of  air  and  completely 
burnt  in  the  outer  checker  brick  chamber.  It  passes  thence  to  the 
flues.  After  a  suitable  period  of  scavenging,  steam  is  admitted  at 
the  top  of  the  outer  checker  brick  chamber  which  is  now  the 
hottest  part  of  the  unit,  and  is  superheated  whilst  passing 
through  the  chamber.  It  then  passes  through  the  reduced  ore 
from  the  bottom  upwards.  The  steam-hydrogen  mixture  is  drawn 
off  at  the  top  of  the  contact  mass  and  is  led  to  the  purification 
system.  With  such  an  arrangement  of  contact  bed  and  checker- 
brick  combustion  chambers  it  is  possible  to  reverse  the  course 
of  combustion  and  the  directions  of  gas  and  steam  flow.  In  this 
way  a  more  even  temperature  distribution  throughout  the  bed  is 
secured  than  is  possible  with  a  single  combustion  chamber  cen- 
trally placed. 

For  such  units,  a  cycle  similar  to  that  adopted  in  the  multi- 
retort  system  also  holds.  The  reducing  phase  normally  occu- 
pies 20  minutes  and  the  steaming  phase  10  minutes.  The  same 
considerations  hold  with  regard  to  modifications  of  procedure 
in  the  two  operations  as  in  the  multi-retort  type  and  these  will 
be  discussed  in  detail  in  later  sections. 

It  is  apparent  that,  with  such  type  of  plant,  renewal  of  con- 
tact material  is  more  easily  effected  than  in  the  case  of  a  multi- 
retort  unit.  It  is  doubtful,  however,  whether  the  same  high  purity 
of  gas  can  be  secured  with  this  type,  since  scavenging  of  the 
checker  brick  chambers  in  addition  to  the  ore  annulus  is  neces- 
sary. 

The  patent  to  Griggs17  embodies  the  latest  features  of  the 
single  retort  unit  as  evolved,  during  the  war,  from  large  scale 

"U.  S.  P.  1,225,262,  1,225,263  or  1,225,264/1917. 
"  B.  P.  142,882/1920. 


HYDROGEN  FROM  STEAM 


39 


/=• 


FIG.  V.     Single  Retort  Unit  for  Steam-Iron  Process. 


40  INDUSTRIAL  HYDROGEN 

operation  of  the  process.  According  to  the  patent  claims,  the 
invention  consists  in  providing  a  combustion  chamber  D  (Fig. 
V)  at  the  lower  end  of  the  inner  heating  space  and  below  the 
bottom  level  of  the  ore  in  the  ore  chamber,  the  streams  of  air 
and  reducing  gas  being  led  in  at  the  bottom  of  the  combustion 
chamber  by  relatively  inclined  passages  E  to  cause  intermingling 
immediately  the  gases  enter  the  chamber.  Complete  combustion 
of  the  gases  is  thus  caused  to  take  place  within  the  combustion 
chamber  and  below  the  level  of  the  ore  chamber,  the  inner  heat- 
ing checker-brick  work  chamber  J  being  used  for  heat  storage 
only.  In  order  to  facilitate  still  further  the  rapid  mixing  of  the 
air  and  gas  the  air  supply  may  be  given  a  circular  motion  by 
arranging  a  tangential  connection  to  the  air  box  as  at  F  in  the 
accompanying  diagram.  The  combustion  chamber  D  may  be  con- 
structed of  such  shape  that  it  will  assist  in  promoting  mixture 
and,  thereby,  combustion  of  the  gases,  by  increasing  the  thickness 
of  the  fire-brick  walls  towards  the  upper  end  of  the  chamber. 
The  inner  side  of  the  liner  A  is  protected  by  a  firebrick  lining 
I  which  causes  the  life  of  the  inner  metal  liner  to  be  greatly 
lengthened. 

Scavenging  is  carried  out  by  steam  introduced  through  the 
reducing  gas  inlet  C  and  passing  successively  through  the  inner 
checker-work  J,  the  ore  annulus  B  and  the  outer  air-chamber 
to  the  waste-gas  vents  K.  The  steam  for  the  hydrogen  make  is 
then  introduced  at  K  the  vents  being  now  closed  and  the  hydro- 
gen withdrawn  through  P. 

The  excess  of  combustible  gas  employed  in  the  reducing  phase 
may  be  burnt  by  auxiliary  air  supplies  introduced  into  the  outer 
chamber  by  the  pipes  M  and  N,  generating  additional  heat  in 
the  outer  annulus  and  thereby  conserving  the  temperature  of  the 
iron  contact  mass. 

With  such  a  method  of  procedure  it  is  claimed  that  the  an- 
nulus of  ore  may  be  maintained  readily  at  an  even  and  not  ex- 
cessive reaction  temperature,  whereas,  in  the  older  forms,  the  va^- 
riation  in  temperature  along  the  length  of  the  annulus  was  very 
marked.  Griggs 18  states  that  with  such  an  apparatus,  hydrogen 
production  can  be  carried  out  more  satisfactorily  than  with  any 
of  the  retort  type  processes. 

"  Hydrogen  Manual,  Part  II. 


HYDROGEN  FROM  STEAM  41 

The  patent  to  Abbott,19  assigned  to  the  Improved  Equipment 
Co.  of  New  York,  shows  how,  by  a  series  of  4  single  retort  units 
and  a  special  heating  chamber,  a  continuous  production  of  hy- 
drogen by  this  system  may  be  achieved. 

The  concentric  ore  and  combustion  chambers  of  the  Messer- 
schmitt  plant  are  all  separated  in  the  patent  of  Bosch,20  which 
represent  the  modification  of  the  steam-iron  process  as  adver- 
tised by  the  Berlin  Anhaltische  Maschinenbau  Aktien  Gessel- 
schaft.  In  this  patent  three  separate  shafts  are  used,  two  checker 
brick  preheaters  and  one  ore  shaft.  The  reducing  gas  is  first 
passed  through  the  ore  and  then  completely  oxidised  with  the 
addition  of  air  in  one  of  the  combustion  chambers.  The  other 
combustion  chamber  is  then  used  to  superheat  the  steam  prior 
to  passage  through  the  reduced  ore.  In  the  subsequent  cycle, 
the  role  of  the  two  preheaters  is  reversed  and  so,  upon  completion 
of  the  two  phases  of  reduction  and  steaming,  the  state  of  the  sys- 
tem is  the  same  as  at  the  beginning  of  such  phases. 

Various  other  modifications  of  the  single  retort  unit  are  to  be 
noted.  One  is  due  to  Schaefer,21  who  insists  that  to  avoid  over- 
heating in  the  contact  mass  by  burning  gases  directly  in  the  ore 
more  than  the  theoretical  amount  of  air  must  be  mixed  with  the 
water-gas.  Spitzer 22  uses  a  mixture  of  producer  gas  and  excess 
of  air  to  raise  the  temperature  of  the  contact  mass,  uses  water- 
gas  for  reducing  the  oxide  of  iron  and  burns  the  spent  water-gas 
to  superheat  the  steam.  Moses  23  has  an  apparatus  which  is  a 
combination  in  one  unit  of  several  features  of  the  Messerschmitt 
and  Bosch  types  of  plant,  and  aims  at  evenness  of  temperature 
distribution  by  complete  freedom  of  action  with  regard  to  course 
of  gas  combustion  and  alternation  of  direction  of  gas  flow. 

Operational  Procedure. — In  starting  a  plant  from  cold  the 
procedure  will  vary  with  the  type  of  generator  employed.  A 
multi-retort  unit  with  built-in  producer  will  be  brought  to  re- 
action temperature  by  starting  the  producer  and  burning  the 
gas  within  the  combustion  chamber.  With  the  Lane  type  of  gen- 
erator, water-gas  would  be  burned  outside  the  retorts  until  they 

19  TJ.  S.  P.  1,345,905/1920. 

20  U.  S.  P.  1,102,716/1914. 

21  U.  S.  P.  1,144,  730/1915. 

22  U.  S.  P.  1,118  595/1914. 

23  U.  S.  P.  1,306,831/1919. 


42  INDUSTRIAL  HYDROGEN 

are  sufficiently  hot  to  promote  combustion  of  a  water-gas-air 
mixture  within  the  retorts.  The  heat  of  reaction  is  thereby  ab- 
sorbed by  the  contact  mass  which  finally  achieves  a  tempera- 
ture sufficiently  elevated  for  reduction  to  be  carried  on.  In  the 
single-retort  type,  the  reaction  material  is  raised  to  reaction  tem- 
perature by  combustion  of  the  reducing  gas  with  air  within  the 
reaction  system.  Thereafter,  in  every  case,  a  normal  cycle  of  re- 
duction and  oxidation  may  be  maintained. 

The  Reduction  Phase. — The  normal  reducing  agent  employed 
is  blue  water-gas.  Other  technical  gases,  such  as  air-producer 
gas,  semi-water-gas  and  special  producer  gases  with  high  carbon 
monoxide  content  have  all  been  tried  and  used,  but  they  are  all 
inferior  to  blue  water-gas.  This  is  doubtless  due  to  the  high  con- 
centration of  inert  constituents  which  such  gases  contain  whereas, 
with  water-gas,  these  inert  constituents  are  reducible  to  a  mini- 
mum. The  reduction  process  is  by  no  means  a  rapid  one  and 
hence  a  high  concentration  of  reducing  agent  is  desirable.  As 
to  specifications  in  the  water-gas  employed,  opinion  is  unanimous 
as  regards  the  necessity  of  employing  gas  free  as  far  as  possible 
from  dust  and  from  sulphur  compounds.  Therefore,  the  water- 
gas  is  submitted  to  a  rigorous  scrubbing  in  a  coke-filled  scrubber 
condenser  and  is  then  freed  from  sulphuretted  hydrogen.  The 
normal  iron-oxide  box  treatment  of  the  gas  industry  is  usually 
employed  for  this  purpose — passage  of  the  gas  through  large 
rectangular  or  circular  boxes  filled  with  a  mixture  of  moist  hy- 
drated  oxide  of  iron  and  wood  shavings  to  lighten  the  material — 
a  ten-minute  time  of  contact  being  sufficient.  Some  very  recent 
investigations,24  have  for  their  object  the  removal  of  the  bulk 
of  the  sulphuretted  hydrogen  by  scrubbing  with  a  suspension  of 
iron  hydroxide  in  water,  to  be  followed  by  a  final  purification  by 
the  normal  box  treatment.  In  this  way  the  heavy  cost  asso- 
ciated with  the  charging  and  discharging  of  the  iron-oxide  box 
system  may  be  reduced. 

Removal  of  dust  prevents  choking  of  the  retorts  with  non- 
active  or  with  carbonaceous  material.  Removal  of  the  sul- 
phuretted hydrogen  increases  the  efficiency  of  the  process  by 
minimising  the  extent  to  which  the  iron  contact  mass  is  con- 
verted into  sulphide.  This  is  harmful  for  several  reasons.  Sul- 

14  See  for  example:     Evans,  Gas  Record,  1919,  15,  215. 


HYDROGEN  FROM  STEAM  43 

phide  of  h-on  tends  to  promote  fusion  of  the  reaction  material 
at  the  temperatures  employed.  Also,  the  protective  coating  of 
sulphide  decreases  the  extent  of  active  surface.  Further,  it  re- 
acts partially  with  the  steam  and  so  introduces  sulphur  gases 
into  the  hydrogen  produced  in  the  succeeding  steaming  opera- 
tion. It  must  be  observed,  however,  that  the  iron-oxide  box 
treatment  does  not  remove  all  sulphur  compounds  from  the  water- 
gas.  Carbon  disulphide  and  organic  sulphur  compounds  in  small 
concentrations  remain  in  the  water-gas  and  these  produce,  to  a 
lesser  extent,  however,  the  disadvantages  associated  with  the  use 
of  a  gas  containing  sulphuretted  hydrogen.  Indeed,  it  is  prob- 
ably through  hydrogen  sulphide  that  the  effect  proceeds  since, 
under  the  given  conditions,  the  catalytic  action 

CS2  +  2H20  =  C02  +  2H2S 

readily  occurs  on  passage  of  water-gas  containing  carbon  disul- 
phide through  the  iron  contact  mass. 

Specifications  on  carbon  monoxide,  carbon  dioxide  and  hydro- 
gen contents  of  the  water-gas  vary  largely,  and  are  adapted  to  the 
mode  of  operation  employed.  Thus,  in  one  case,  a  low  reaction 
temperature  is  employed  and  a  water-gas  containing  a  minimum 
of  carbon  dioxide,  averaging  3  per  cent,  is  employed.  In  this  case 
efficient  reduction  is  attained  and  a  low  ratio  of  water-gas  used 
to  hydrogen  produced  is  possible,  thus  making  for  economy  of 
operation. 

It  is  apposite,  at  this  point,  to  amplify  the  theoretical  bases 
underlying  this  concept  of  water-gas-hydrogen  ratio  since  the 
amount  of  water-gas  consumed  in  the  reduction  process  is  an  im- 
portant factor  in  the  economy  of  the  process.  As  pointed  out 
earlier  in  the  chapter,  the  reactions  occurring  are  equilibrium 
processes,  which,  at  the  temperatures  involved,  are  incomplete  in 
either  direction.  If  the  simplifying  assumptions  be  made  that  the 
reactions  occurring  are 


(a)  Fe304+   CO  =  3FeO  +   C02 
(a')  Fe304  +    H2  =  3FeO  +  H20 

(b)  3FeO  +  3CO  =  3Fe    +  3C02 
(b')  3FeO  +  3H2  =  3Fe  !  +  3H20 

and  that  they  occur  to  equal  extent  as  regards  reaction  of  carbon 
monoxide  and  hydrogen  it  may  be  calculated,  from  the  equilib- 


44 


INDUSTRIAL  HYDROGEN 


rium  data  given  earlier,  that,  of  a  water-gas  composed  of  equal 
volumes  of  hydrogen  and  carbon  monoxide,  the  following  per- 
centages of  these  gases  would  be  consumed  in  the  reduction  proc- 
ess when  equilibrium  was  established,  at  various  operating  tem- 
peratures. For  more  exact  figures  see  Appendix  I. 

Fe304-FeO  REACTION 


Temperature   % 

H.2  Consumed 

%  CO  Consumed 

Water-Gas:  H2 

650 
750 
850 

42 
56 
66 

64 
70 
80 

1.8 
1.6 
1.4 

FeO-Fe  REACTION 


Temperature 

%  H2  Consumed 

%CO  Consumed 

Water-Gas:  H., 

650 
750 
850 

30 
33 
41 

41 
40 
35 

2.85 
2.77 
2.63 

Now  the  volume  of  reducing  gas  oxidised  in  the  reduction 
process  represents  also  the  volume  of  hydrogen  subsequently  ob- 
tained in  the  subsequent  steaming  process.  Hence,  it  is  easy  to 
calculate  the  volume  of  hydrogen  produced  from  200  volumes 
of  water-gas  and  hence  the  ratio  of  water-gas  consumed  to 
hydrogen  which  may  be  theoretically  produced.  These  calcu- 
lations are  tabulated  in  the  last  column.  It  is  at  once  evident 
that  it  would  be  more  economical  of  water-gas  to  work  on  the 
Fe304-FeO  cycle  and  this  is  largely  recommended  in  practice. 
It  must  be  observed,  however,  as  reference  to  the  equations  at 
once  shows,  that  only  one-fourth  the  yield  of  hydrogen  per 
unit  of  ore  is  obtained. 

Too  much  stress  must  not  be  laid  on  such  calculations,  how- 
ever, since  they  were  made  with  certain  simplifying  assumptions. 
It  was  assumed  that  equilibrium  conditions  hold  over  the  whole 
reducing  phase,  which  is  not  always  true,  especially  towards  the 
end  of  a  reduction  phase  when  the  bulk  of  the  surface  oxide  has 
been  reduced.  Furthermore,  it  was  assumed  that  hydrogen  and 
carbon  monoxide  were  equally  attacked  whereas  it  is  known 
that  hydrogen  is  the  more  reactive  reducing  agent.  Owing,  how- 


HYDROGEN  FROM  STEAM  45 

ever,  to  the  ready  interaction  of  carbon  monoxide  with  the  steam 
produced  by  the  oxidation  of  the  hydrogen,  according  to  the  equa- 
tion of  the  water-gas  reaction 

CO  +  H20  =  C02  +  H2 

carbon  monoxide  also  disappears  rapidly.  Indeed,  when  meas- 
ured over  a  sufficiently  short  interval  of  time,  the  exit  carbon 
monoxide,  carbon  dioxide,  hydrogen  and  steam  are  present  in  the 
ratios  determined  by  the  equilibrium  constant  of  this  water-gas 
reaction  at  the  operating  temperature  (see  Chapter  III). 

[CO]   [H20] 


[H2]     [CO,] 

But,  since  the  amount  of  oxide  of  iron  to  be  reduced  becomes  less 
and  less  as  the  reducing  phase  continues,  the  relative  amounts  of 
carbon  dioxide  and  steam  formed  become  less  and  less.  This 
continuously  changing  extent  of  reaction  with  time  vitiates  any 
complete  simple  theoretical  treatment.  The  point  of  view  pre- 
sented will  therefore  be  regarded  as  sufficient  to  indicate  in  a 
qualitative  manner  the  reasons  why  considerably  more  than  unit 
volume  of  water-gas  must  be  consumed  to  produce  one  volume 
of  hydrogen. 

In  the  later  stages  of  the  reducing  period,  when  a  large  sur- 
face of  reduced  iron  is  exposed  to  the  incoming  gases,  another 
catalytic  action  is  rapid  at  'the  prevailing  temperatures.  Re- 
duced metals,  more  especially,  nickel  and  iron,  catalyse  the  re- 
versible reaction 

2CO  =  C02  +  C. 

At  a  given  temperature  definite  concentrations  of  the  two  gases 
are  in  equilibrium  with  carbon.  If  carbon  monoxide  be  in  ex- 
cess, reaction  occurs  in  the  direction  of  equilibrium  with  simul- 
taneous deposition  of  carbon.  It  is  in  this  way  that  carbon  is 
introduced  into  the  contact  mass.  The  carbon  thus  deposited  is 
extremely  reactive  and  yields,  in  the  subsequent  steaming  phase, 
both  carbon  monoxide  and  carbon  dioxide,  the  former  of*which 
is  frequently  a  very  detrimental  impurity  in  hydrogen. 

To  prevent  deposition  of  carbon,  various  devices  are  used. 
Thus,  the  Dellwick-Fleischer  25  purity-steam  process  seeks  to  ef- 

25  B.   P.  21,479/1908. 


46  INDUSTRIAL  HYDROGEN 

feet  this  by  introducing  steam  along  with  the  reducing  gas.  In 
this  manner,  owing  to  the  operation  of  the  water-gas  equilibrium 

CO  +  H20  =  C02  +  H2 

the  reducing  agent  becomes  mainly  hydrogen  and  the  ratio  of 
C02  :  CO  is  kept  high,  thus  diminishing  the  tendency  towards 
decomposition  of  carbon  monoxide.  Maxted,26  for  the  same 
purpose,  utilises  a  reducing  gas  containing  a  C02  :  CO  ratio 
definitely  higher  than  that  corresponding  to  the  equilibrium  ratio 
in  the  reaction 

2CO  =  C02  +  C. 

The  presence  of  carbon  dioxide  to  the  extent  of  at  least  twice  the 
volume  of  carbon  monoxide  is  advised. 

The  same  result  is  achieved  in  the  procedure  adopted  in  the 
most  recent  types  of  Messerschmitt  plant.  The  reducing  agent 
in  this  case  is  a  partially  burnt  water-gas.  The  carbon  dioxide, 
carbon  monoxide  ratio  is  high  and  therefore  prevents  or  reduces 
the  deposition  of  carbon  on  the  reacting  substance. 

From  the  tables  of  gas  consumption  in  the  reducing  phase 
already  given  it  is  obvious,  however,  that  this  prevention  of 
carbon  deposition  is  only  secured  at  the  expense  of  the  ratio  of 
water-gas  consumption  to  hydrogen  produced.  The  expense  item 
for  water-gas  will  be  correspondingly  increased.  Furthermore, 
the  presence  of  carbon  dioxide  and  steam  undoubtedly  cuts 
down  the  rate  at  which  hydrogen  and  carbon  monoxide  act  as 
reducing  agents. 

In  actual  practice,  all  variations  between  the  two  extremes, — 
(a)  water-gas  of  low  carbon  dioxide  content,  with  rapid  and  effi- 
cient reduction  with,  however,  tendency  to  carbon  deposition 
and  (b)  high  concentration  of  carbon  dioxide  with  correspond- 
ing slower  and  less  economic  reduction  with  less  tendency  to 
carbon  deposition — are  to  be  found.  The  actual  procedure  is 
governed  by  many  considerations  both  of  technique  and  of  utili- 
sation of  the  hydrogen. 

Agtual  figures  taken  from  a  hydrogen  plant  operating  on  the 
multi-retort  system  gave  the  following  analyses  for  water-gas 
used,  spent  water-gas  issuing  from  the  retorts  and  the  same 
after  removal  of  the  steam. 

28  B.  P.  12,698/1915;  U.  S.  P.  1,253,622/1918. 


HYDROGEN  FROM  STEAM 


47 


H2 

H20 

CO 

CO., 

N2,  Etc. 

Water-Gas  (dry  basis) 
Spent  Water-Gas  
Spent  Water-Gas  (dry 
basis)   

50 
25 

33.3 

25 

42 
12 

16 

5 
35 

46.3 

3 
3 

4.4 

The  plant  in  question  was  operated  at  a  temperature  averag- 
ing 700°  C.  In  the  Messerschmitt  type  of  plant  similar  figures 
will  be  obtained  for  the  original  water-gas.  For  the  gas  leaving 
the  contact  mass,  there  will  be  a  larger  amount  of  diluent  nitro- 
gen introduced  as  air  in  the  preliminary  partial  combustion  in 
the  checker  brick  chamber.  The  presence  of  this  diluent  nitro- 
gen, lowering  the  partial  pressures  of  the  actual  reducing  gas  as 
well  as  the  utilisation  of  some  of  the  reducing  gas  in  the  com- 
bustion process  inevitably  results  in  a  higher  ratio  of  water-gas 
consumed  to  hydrogen  actually  produced  in  this  method  of  opera- 
tion. 

The  best  practice  in  respect  to  water-gas:  hydrogen  ratio 
over  a  fair  interval  of  time,  in  which  the  variable  activity  of  a 
contact  mass  may  be  noted,  seems  to  yield,  in  multi-retort  units, 
a  figure  of  2.5  :  1.  One  volume  of  hydrogen  is  produced  at  the 
expense  of  two  and  one-half  volumes  of  water-gas.  This  figure 
refers  to  a  plant  containing  many  units  with  as  nearly  as  possible 
continuous  operation.  Stoppages  of  the  plant  raise  this  figure 
considerably,  since,  in  such  cases,  water-gas  has  to  be  consumed 
to  maintain  retort  temperatures  during  stoppages  of  the  plant, 
without  corresponding  hydrogen  yield.  With  decrease  in  plant 
size  and  increased  intermittency  of  working  the  water-gas  con- 
sumption rises  markedly  and  becomes  a  most  serious  cost  item. 
Under  such  conditions  as  much  as  4-5  volumes  of  water-gas  may 
be  consumed. 

For  large-scale  operation  with  high  efficiency  in  respect  to 
water-gas-hydrogen  ratio,  the  use  of  meters  for  both  water-gas 
and  hydrogen  cannot  be  too  strongly  urged.  A  constant  check 
can  be  kept  in  this  manner  on  the  variation  in  efficiency  of  the 
process,  with  accidental  variations  in  temperature,  with  the  vary- 
ing care  with  which  the  plant  is  operated  and  with  the  life  of 
the  reaction  material.  Experience  has  shown  that  such  check  on 
the  process  tends  continuously  towards  high  operating  efficiency. 


48  INDUSTRIAL  HYDROGEN 

Finally,  with  reference  to  the  delivery  of  the  reducing  gas  to 
the  retort  system,  care  is  needed  to  prevent  the  possibility  of  its 
contaminating  the  hydrogen  mains.  The  reducing  gas  is  generally 
driven  from  the  generator,  by  means  of  a  booster,  through  the 
purification  system  to  a  water-gas  holder.  The  head  of  water  in 
the  holder  is  adequate  to  drive  the  gas  through  the  retort  system. 
It  should  be  arranged,  however,  that  this  head  of  water  is  less 
than  that  prevailing  in  the  hydrogen  mains.  Failure  to  observe 
this  has  resulted  in  contamination  much  more  serious  than  that 
due  to  carbon  deposition  in  the  reaction  mass.  R.  &  J.  Demp- 
ster, Ltd.,27  of  Manchester,  England,  provide  a  special  automatic 
pressure  regulating  device  with  their  plant  in  order  to  ensure  the 
attainment  of  this  pressure  distribution. 

The  Steaming  Period. — The  reduction  phase  is  immediately 
succeeded  by  the  steaming  period.  Delivery  of  water-gas  is 
stopped  and  steam  turned  into  the  reaction  system  by  the  opera- 
tion of  a  single  valve  or  a  system  of  valves. 

For  simplicity  of  discussion  a  unit  of  36  retorts,  operated  as 
a  whole  and  not  in  three  sets  of  twelve,  will  be  considered.  With 
the  dimensions  previously  given  (p.  31)  the  internal  volume  of 
the  retorts  is  approximately  160  cubic  feet  and  the  unit  has  a 
capacity  of  3,500  cubic  feet  per  hour  containing  two  10-minute 
steaming  periods.  This  yield  of  3,500  cubic  feet  is  by  no  means 
evenly  distributed  over  the  twenty  minutes  actually  involved. 
As  in  the  reducing  phase,  the  active  surface  rapidly  decreases, 
in  this  case  by  interaction  of  the  iron  or  ferrous  oxide  with  the 
steam.  The  hydrogen  yield,  per  minute  interval,  progressively 
decreases  throughout  the  period  to  an  extent  determined  by  the 
activity  of  the  contact  mass.  With  fresh,  reactive  material  the 
decrease  in  yield  with  time  is  much  smaller  than  with  an  old, 
non-reactive  mass.  In  the  average  case,  a  yield  of  250  cubic 
feet  in  the  first  minute's  steaming  and  one  of  less  than  100  cubic 
feet  in  the  last  minute  will  be  obtained.  The  variation  in  yield 
with  time  may  be  used,  as  well  as  the  water-gas:  hydrogen  ratio, 
as  a  criterion  of  the  reaction  mass. 

The  utilisation  of  the  steam  to  yield  hydrogen  likewise  pro- 
gressively decreases  with  time,  over  the  given  interval.  The  ac- 
tual ratio  of  steam  to  hydrogen  varies  with  varying  practice.  In 
one  case,  in  which  an  average  amount  of  steam  was  consumed, 

«  B.  P.  16,893/1914. 


HYDROGEN  FROM  STEAM  49 

the  steam:  hydrogen  ratio  in  the  first  minute  was  5  :  3  and,  in 
the  last  minute  of  the  run,  as  much  as  7  :  1,  averaging  through- 
out a  ratio  of  3  :  1.  Assuming  a  free  space  of  75  per  cent  inside 
the  retort  system,  the  volume  of  water  gas  in  the  retorts  at  the 
commencement  of  steaming  is 

160  X  75 

=  120  cubic  feet. 

100 

With  a  first  minute  yield  of  250  cubic  feet  of  hydrogen  and  a 
steam:  hydrogen  ratio  of  5  :  3,  it  is  obvious  that 
120      3      60 

X  -  X  —  =  17  seconds. 

250      5         1 

will  be  the  time  approximately  occupied  in  removing  the  spent 
water-gas  from  the  retort  system.  Consequently,  for  a  period, 
varying  from  15  to  30  seconds  in  practice,  after  the  steam  is 
turned  on,  the  gases  swept  out  by  the  incoming  steam  follow  the 
spent  water-gas.  They  are  then  directed  into  the  hydrogen  main. 
By  means  of  this  period  of  "-scavenging"  or  "purging"  the  purity 
of  the  hydrogen  is  materially  increased. 

It  is  not  possible,  however,  to  eliminate  entirely  the  presence 
of  impurities  in  the  hydrogen  produced  by  this  means.  As  out- 
lined in  the  previous  section,  unless  a  special  modification  of  the 
reducing  gas  is  employed,  carbon  is  deposited  on  the  contact 
mass  and  sulphide  of  iron  is  formed.  These  substances  react 
with  the  steam  to  produce  carbon  monoxide,  carbon  dioxide  and 
sulphuretted  hydrogen.  A  closer  examination  of  the  varying 
concentrations  of  carbon  monoxide  and  dioxide  at  different  in- 
tervals of  the  run  has  led  to  an  interesting  elucidation  of  the  conr 
ditions  governing  their  formation.  By  means  of  a  carbon  mon- 
oxide recorder,  Rideal  and  Taylor 28  were  able  to  show  that,  at 
the  beginning  of  the  steaming  phase,  the  carbon  monoxide  was 
present  in  greater  concentration  than  at  the  end  of  a  run.  With 
carbon  dioxide  the  conditions  were  reversed.  Thus,  a  given  sam- 
ple taken  from  the  yield  of  hydrogen  during  the  first  minutes  of 
a  run  showed  a  carbon  monoxide  concentration  of  0.27  per  cent 
while  in  the  last  minutes  of  the  same  run  the  concentration  of 
the  gas  was  only  0.11  per  cent.  Closer  examination  showed  that 
the  relative  concentrations  of  carbon  monoxide  and  carbon  di- 

28  Analyst  1919,  kk,  89. 


50  INDUSTRIAL  HYDROGEN 

oxide  were  governed  by  the  water  gas  equilibrium  at  the  tem- 
perature of  operation 

_  PHZO  x  PCO 


In  the  initial  portion  of  the  run  p-g-  Q/PJJ  is  small,  as  already 
stated.  Hence  PQQ/PCO  *s  corresP°ndingly  large.  At  the  end 
of  a  run  where  the  ratio,  steam  to  hydrogen,  is  very  high,  the  ratio 
of  carbon  monoxide  to  dioxide  is  low.  It  is  evident  that  the  iron- 
iron  oxide  contact  mass  is  acting  as  catalyst,  in  the  water-gas 
reaction,  for  the  gases  produced  by  interaction  of  the  steam  with 
the  iron  and  the  carbon  deposited  in  the  retort  system.  The  car- 
bon produced  during  the  reducing  period  is  always  greater  in 
amount  than  the  carbon  which  interacts  with  steam  in  the  sub- 
sequent operation.  An  accumulation  of  carbon  therefore  occurs, 
the  removal  of  which  is  effected  by  aeration  as  later  outlined. 
The  same  also  is  true  of  the  accumulation  of  sulphur  as  iron  sul- 
phide, which  reacts  with  steam  and  gives  the  hydrogen  a  concen- 
tration of  sulphuretted  hydrogen  averaging  0.05  per  cent. 

From  these  considerations  it  follows  that  the  purity  of  the 
gas  produced  in  the  hydrogen  generator  is  dependent  on  the  thor- 
oughness of  the  scavenging  process,  the  state  of  the  retort  mass 
in  respect  to  carbon  and  sulphur  accumulations,  the  amount  of 
steam  used  in  the  steaming  process  and  the  temperature  at  which 
reaction  occurs.  An  average  product  with  a  steam:  hydrogen 
ratio  of  3  :  1  and  an  operating  temperature  of  650°  C.  gave  the 
following  figures: 

H2  =  98.5  to  99%  ;  C02  =  0.5  to  1%  ;  CO  =  0.2  to  0.3%  ; 
H2S  ==  0.05%  ;  N2  =  0  to  0.25%. 

In  case  carbon  deposition  is  prevented  by  one  or  other  of  the 
methods  quoted,  the  purity  of  the  gas  is  considerably  increased. 
Thus,  Maxted  quotes  29  for  the  hydrogen  yielded  by  his  modifica- 
tion of  the  steam-iron  process,  a  gas  of  the  composition: 

H2    =99.94 
CO  =nil 
C02  =  nil 
N2    =0.06. 

"J.  800.  Chem.  Itid.,  1917,  S6t  779. 


HYDROGEN  FROM  STEAM  51 

For  the  attainment  of  this  high  degree  of  freedom  from  traces  of 
air  or  its  components  it  is  necessary,  states  Maxted,  to  employ 
heated  feed  water  for  the  boiler  which  supplies  steam  for  the  hy- 
drogen plant  and  to  install  tubular  condensers  in  preference  to 
open  water  scrubbers. 

For  the  steaming  process  it  is  advisable  to  employ  dry  steam, 
and  a  working  pressure  of  60  to  80  Ibs.  is  usual.  By  superheating 
the  steam  still  further  considerable  advantage  in  operation  results 
both  as  to  yield  of  hydrogen  and  diminution  of  disintegration  of 
the  contact  mass.  In  the  Lane  system  and  modifications  of  this 
type  it  is  usual  to  use  the  steam  at  the  pressure  named  without 
any  superheat.  The  exothermicity  of  the  reaction  is  sufficient  to 
raise  the  steam  to  reaction  temperature  when  the  retorts  are  ex- 
ternally heated  and  even  to  bring  about  a  small  increase  in  the 
temperature  of  the  retort  mass.  In  the  single  retort  unit,  the 
steam  is  partially  superheated  in  the  checker-brick  chamber  sur- 
rounding the  contact  material. 

The  crude  hydrogen-steam  mixture,  after  leaving  the  genera- 
tor, passes  to  a  scrubber  condenser  where  it  is  freed  from  steam 
and  then  to  a  purification  system  in  which  the  sulphuretted  hy- 
drogen and  carbon  dioxide  are  removed.  Removal  of  residual 
carbon  monoxide  requires  a  special  process.  In  the  earlier  plants, 
a  scrubber  condenser  was  attached  to  each  generator  unit  for  re- 
moval of  the  steam.  This  involves  an  unnecessary  duplication  of 
plant  and  so,  in  more  modern  installations,  one  large  scrubber  to 
several  units  is  employed.  The  scrubbers  are  generally  coke- 
filled  towers  up  which  the  gas  mixture  passes,  with  water  flowing 
downwards  over  the  coke,  counter-current  to  the  gas.  For  re- 
moval of  the  sulphuretted  hydrogen  and  carbon  dioxide,  proce- 
dure varies  in  different  plants.  In  some  plants  both  impurities 
are  removed  simultaneously  by  passage  of  the  gas  through  a  sys- 
tem of  lime  boxes  such  as  were  used  formerly  in  the  gas  indus- 
try and  of  the  same  type  as  are  used  in  the  removal  of  sulphu- 
retted hydrogen.  This  treatment  is  economical  of  plant  since 
only  one  set  of  four  lime  boxes  are  required  in  addition  to  the 
booster  necessary  to  drive  the  gas  through  the  purification  sys- 
tem. On  the  other  hand  this  method  of  purification  is  costly  both 
in  material  and  labor.  The  lime  cannot  be  renewed  owing  to 
the  formation  of  calcium  sulphide.  The  labor  cost  is  high  since 


52  INDUSTRIAL  HYDROGEN 

the  action  is  mainly  confined  to  the  surface  of  the  material  and 
frequent  renewal  of  the  lime  is  necessary. 

The  alternative  procedure  in  respect  to  purification  is  to  re- 
move the  sulphuretted  hydrogen  first  by  iron  oxide  box  treatment 
or  by  treatment  with  an  iron  oxide  sludge  followed  by  the  usual 
box  treatment  for  the  final  traces.  The  carbon  dioxide  is  then 
removed  in  scrubbers  using  caustic  soda  as  the  absorbent.  For  a 
large  plant  this  alternative  procedure  is  the  more  economical, 
especially  if  the  spent  soda  absorbent  be  causticised  and  so  util- 
ised continuously  in  the  purification  system.  Patents  to  the 
Badische  Co.  (D.  R.  P.  302,555  and  303,292/1916)  cover  the  use 
of  aqueous  suspensions  of  iron  oxide  for  the  removal  of  the  bulk 
of  the  sulphides  followed  by  the  use  of  alkaline  suspensions  of 
iron  oxide  containing  oxalic  acid  for  the  last  traces.  Revivifica- 
tion of  the  spent  liquor,  in  both  cases,  by  blowing  air  through  the 
sludge,  is  claimed.  It  is  obvious  that  such  a  combination  of 
neutral  and  alkaline  absorbing  liquors  would  suffice  for  both  sul- 
phuretted hydrogen  and  carbon  dioxide  removal. 

Aeration. — The  removal  of  carbon  and  sulphur  accumulations 
by  "burning-off"  in  a  current  of  air,  follows  a  steaming  phase  at 
regulated  intervals.  The  frequency  of  the  process  is  governed 
by  the  standard  of  hydrogen  purity  to  be  maintained.  Over  the 
temperature  range  in  question  oxidation  is  very  energetic.  Sul- 
phur dioxide  and  carbon  dioxide  are  the  principal  gaseous  prod- 
ucts of  oxidation  and  the  magnetic  iron  oxide  itself  undergoes 
conversion  to  ferric  oxide 

4Fe304  +  02  =  6Fe203. 

The  increase  in  temperature  of  the  mass  due  to  oxidation  is 
marked  and  the  admission  of  air  must  be  regulated  so  as  to  avoid 
local  overheating.  By  carrying  out  this  process  immediately 
after  the  steaming  phase,  this  can  be  done  and  the  danger  of 
forming  an  explosive  mixture  within  the  retorts  considerably  di- 
minished. On  completion  of  the  aeration  process  it  is  also  advis- 
able to  sweep  out  the  air  with  steam  before  turning  the  reducing 
gas  into  the  system  again.  By  this  method  of  procedure  the 
operation  can  be  conducted  with  perfect  safety. 

To  render  the  burning-off  process  more  complete,  Blair  and 
Ferguson30  have  recently  patented  the  use  of  enriched  air  ob- 

•°B.  P.  143,064/1920. 


HYDROGEN  FROM  STEAM  53 

tained  by  adding,  to  the  air  normally  employed,  oxygen  from 
suitable  source.  It  may  be  presumed  that  the  extra  purity  of  the 
hydrogen  thus  obtained  compensates  for  the  increased  cost  of  the 
enriched  air  employed. 

The  Thermal  Balance  of  the  Process. — From  the  usual  ther- 
mal data  for  the  reactions  of  the  steam-iron  process: 

Fe304  +  2CO  +  2H2  =  3Fe  +  2C02  +  2H20  — 18,000  calories 

steam 

3Fe  +  4H20  =  Fe304  +  4H2  +  38,400  calories 


steam 


it  is  evident  that  the  whole  process  should  be  exothermic,  since 
the  loss  of  heat  in  the  reduction  process  is  outbalanced  by  the 
heat  evolution  in  the  steaming  phase. 

The  problem,  however,  is  by  no  means  so  simple  as  such  a 
statement  would  indicate.  In  the  first  place  the  data  refer  to 
reaction  at  room  temperatures,  whereas  the  reaction  occurs  in 
the  interval  650-850°  C.  Secondly,  the  above  equations  imply 
that  the  alternation  is  between  metallic  iron  and  magnetic  oxide 
of  iron,  whereas  test  shows  that  a  marked  amount  of  ferrous  oxide 
is  present  after  a  reduction  phase.  Furthermore,  the  first  equa- 
tion implies  that  carbon  monoxide  and  hydrogen  are  equally  con- 
sumed in  the  reduction  process,  whereas,  as  was  previously 
pointed  out,  a  greater  proportion  of  carbon  monoxide  is  ap- 
parently used  up.  This  undoubtedly  arises  from  the  setting  up 
of  the  water-gas  equilibrium  in  the  gases  as  they  leave  the  con- 
tact mass,  since  hydrogen  is  known  to  reduce  oxide  of  iron  more 
rapidly  than  does  carbon  monoxide. 

A  detailed  analysis  of  each  of  these  separate  factors  in  the 
question  of  thermal  balance  leads  to  a  very  complex  thermo- 
chemical  problem,  the  unsatisfactory  nature  of  which  is  empha- 
sized by  the  uncertainty  which  attaches  to  the  equilibrium  data 
of  the  several  gases  and  the  oxides  concerned  (see  p.  25).  A 
simpler  method  of  analysis  is  therefore  substituted. 

It  is  apparent  that  the  heat  required,  at  any  temperature,  for 
reduction  of  magnetic  oxide  of  iron  by  hydrogen  to  any  lower 
state  of  oxidation  will  be  exactly  equal  to  that  evolved  in  the 
subsequent  reconversion  of  the  material  to  the  ferrous- ferric  con- 
dition in  presence  of  steam.  From  the  equations 


54  INDUSTRIAL  HYDROGEN 


Fe304  +  4CO  =3Fe     +  4C02 
3Fe     +  4H20  =  Fe3O4  +  4H2 

or  from  the  corresponding  equations  for  ferrous  oxide  formation 
it  is  also  evident  that  for  every  molecule  of  carbon  monoxide  used 
in  the  reducing  stage  a  molecule  of  steam  is  used  in  the  oxidation 
stage,  so  that  the  net  thermal  change  involved  is  the  heat  of 
the  reaction 

CO  +  H20  =  C02  +  H2 

at  the  temperature  of  operation.  This  can  be  accurately  cal- 
culated at  any  temperature  from  the  thermal  data  for  the  heats 
of  formation  of  these  gases  and  from  their  specific  heats,  all  of 
which  magnitudes  are  known  with  great  exactness.31  Recent 
values  for  these  quantities  give  a  heat  of  reaction  at  15°  C.  of 
10,500  calories  and  at  any  other  temperature  t°  C.  the  heat  of 
reaction  is  deducible  from  the  equation 

Qt  =  10,500  +  (t  -  15)  (-  0.535  -  0.0028t  +  0.95  X  10-6t2  + 
0.1  X  10-9t3) 

At  the  average  temperature,  700°  C.,  of  a  steam-iron  process  unit, 
this  gives  a  result 

Q700  =  10,500  +  685  (-  0.535  -  0.0028  X  700  +  0.95  X  10'6  X 

7002  +  0.1  X  10-9  X  7003) 

=  10,500  +  685  (-  0.535  -  1.96  +  0.46  +  0.0343) 
=  10,500  +  685  (-  2.00)  =  10,500  -  1,370 
=    9,130  calories. 

For  every  gram  molecule  of  carbon  monoxide  used  up  in  the  re- 
ducing phase  (which  may  readily  be  determined  from  analysis  of 
the  water-gas  employed  and  spent  water-gas  leaving  the  retorts) 
the  net  positive  thermal  change  is  9,130  calories,  when  the  re- 
action temperature  is  700°  C.  Transposed  into  the  units  em- 
ployed in  industry  this  amounts  to  45.7  B.  th.  U.'s  per  cubic  foot 
of  carbon  monoxide  (at  20°  C.  and  760  mm.  pressure),  when 
the  reaction  is  carried  out  at  a  temperature  of  700°  C.  This 
value  decreases  slowly  with  increase  of  temperature.  At  1,000° 
C.,  however,  it  is  only  some  10  per  cent  less. 

Reference  to  figures  given  in  the  preceding  sections  of  this 
chapter  shows  that,  of  100  volumes  of  water-gas,  approximately 

"  Siegel  :  Z.  phyaik.  Chem.,  1914,  87,  641. 


HYDROGEN  FROM  STEAM  55 

30  volumes  of  carbon  monoxide  and  25  volumes  of  hydrogen 
suffer  oxidation  in  their  passage  through  a  retort  system  at  a 
working  temperature  of  about  700°  C.  For  the  production  of  1 
volume  of  hydrogen,  therefore,  the  water-gas  consumed  is 

100  100 

-  =  —  =1.8  volumes.  Furthermore,  three  volumes 
30  +  25  55 

of  steam  are  used  to  produce  one  volume  of  hydrogen.  Conse- 
quently, in  the  oxidation  of  one  volume  of  carbon  monoxide  dur- 
ing the  reducing  phase,  the  volume  of  water-gas  passed  through 

100 

the  system  is   -  =  3.3  volumes  of  water-gas  and  subsequently 
30 

100  3 

-    X  -  =  5.5  volumes  of  steam  are  used  to  oxidise  the 
30  100 


iron  or  ferrous  oxide  formed  in  the  reducing  phase.  The  mean 
molecular  heats  of  water-gas  and  steam  are  calculable  from  the 
equations 

CP:H2  =  6.685  +  0.00045  1 
CpiCO  =  6.885  +  0.00045  1 
Cp  :  H20  =  8.050  +  0.0005  1  +  0.2  X  10"9  13. 

With  these  data,  the  heat  required  to  raise  3.3  gram  molecules 
of  water-gas  (1.65  gram  molecules  H2  +  1.65  gram  molecules  CO) 
from  15°  to  700°  and  5.5  gram  molecules  of  steam  from  100°  to 
700°  may  be  shown  to  be 

685(3.3(6.785  +  0.00045  X  700)  )  +  600(5.5(8.050  +  0.0005  1  + 

0.2X10-H3)  ) 
=  16,050  +  27,930 
=  43,980  calories: 

It  is  therefore  evident  that,  while  the  chemical  reactions  oc- 
curring at  700°  C.  show  a  small  positive  thermal  balance  of  9,130 
calories  per  gram  molecule  of  carbon  monoxide  oxidised  in  the  re- 
ducing phase,  this  heat  of  reaction  is  not  sufficient  to  raise  the 
temperature  of  the  incoming  water-gas  and  steam  to  the  reaction 
temperatures.  The  calculations  made,  clearly  show  the  neces- 
sity for  heat  other  than  that  obtainable  from  the  total  reaction 
process.  The  devices  previously  detailed,  namely,  the  external 


56  INDUSTRIAL  HYDROGEN 

heating  of  the  retorts,  combustion  of  some  of  the  water-gas  within 
the  retort  system,  superheating  of  the  incoming  water-gas  and 
steam  are  all  methods  whereby  the  heat  of  reaction  is  assisted  in 
supplying  the  heat  required  to  raise  the  gases  employed  to  the 
reacting  temperatures  or  to  keep  the  contact  mass  at  the  de- 
sired heat. 

The  efficiency  of  such  methods  of  maintaining  reaction  tem- 
perature can  now  readily  be  calculated  in  the  multi-retort  proc- 
ess, in  which  the  spent  water-gas,  after  removal  of  the  steam, 
is  all  burned  on  the  outside  of  the  retort.  In  the  case  thus  far 
considered  the  spent  water-gas  has  the  composition:  H2  =  25% ; 
H20  =  25% ;  C02  —  35% ;  CO  =  12%.  In  addition  to  this  spent 
gas  the  first  fraction  of  the  hydrogen  produced,  the  hydrogen 
employed  in  the  "scavenging"  of  the  retort  system,  is  also  burned 
around  the  retorts.  About  10  per  cent  of  the  hydrogen  yield  is 
so  consumed.  In  the  case  under  consideration  this  would  be  10 
per  cent  of  55  volumes  produced  after  the  reduction  process, 
which  involved  30  volumes  of  carbon  monoxide  and  25  volumes 
of  hydrogen. 

Now,  since 

2H2  +  02  =  2H20  +  116,000  calories 
and  2CO  +  02  =  2C02  +  136,000  calories 

the  furnace  efficiency  is  readily  shown  to  be 

(43,980  —  9,130)  X  30  X  2  X  100 

—  40.5  per  cent. 

(25  +  5.5)  X  116,000  +  12  X  136,000 

Expressed  otherwise,  60  per  cent  of  the  heat  generated  on  the  out- 
side of  the  retorts  in  a  multi-retort  system  is  not  utilised  in  the 
reaction  process. 

This  result  derived -from  theoretical  considerations  and  ex- 
perimental data  on  water-gas  and  steam  consumption  is  familiar 
to  anyone  who  has  had  control  of  a  steam-iron  process  multi- 
retort  unit.  A  major  portion  of  the  external  heat  generated  is 
radiated  into  the  surrounding  atmosphere.  The  excessive  amount 
of  this  heat  loss  is  the  more  remarkable  when  it  is  remembered 
that  no  provision  for  possible  heat  exchange  between  inlet  and 
exit  gas  or  steam  has  been  assumed.  It  is  safe  to  say  that,  of  the 
net  thermal  deficiency  on  the  whole  reaction  (inclusive  of  heat 
required  to  raise  the  incoming  gas  or  steam  to  reaction  tempera- 


HYDROGEN  FROM  STEAM  57 

tures)  probably  75  per  cent  could  be  provided  by  heat  exchange. 
Assuming  such  a  figure,  it  follows  that  the  thermal  efficiency 
of  the  process  would  be  of  the  order  of  8-10  per  cent,  in  which 
case  90  per  cent  of  the  heat  available  in  the  spent  water-gas  is 
lost. 

An  approximate  experimental  check  on  these  figures  is  given 
by  some  determinations  of  Lunden  and  Thorsell  in  Sweden  who 
calculated  the  radiation  from  a  plant  producing  4,000  cubic  feet 
of  hydrogen  per  hour.  The  radiation  was  determined  to  be  of 
the  order  of  470,000  Kilogram  calories  per  hour.  Assuming  the 
calorific  value  of  water-gas  to  be  75  Kilogram  calories  per  cubic 
foot,  this  corresponds  to  the  consumption  of  6,400  cubic  feet  of 
water-gas,  or  1.6  volumes  of  water-gas  per  volume  of  hydrogen 
produced.  This  is  of  the  order  of  66  per  cent  of  the  total  water- 
gas  used  in  the  process. 

Record  has  already  been  made  of  the  efforts  to  minimise 
heat  losses  by  the  use  of  a  single  ore  chamber  instead  of  a  mul- 
tiple retort  system.  No  very  considerable  economies  in  water- 
gas  consumption  have,  however,  been  recorded  as  a  result  of  their 
use.  Possibly  this  is  because  of  the  difficulty  of  utilising  spent 
water-gas  largely  diluted  with  nitrogen,  as  is  the  gas  after  use 
as  a  reducing  agent  in  this  type  of  plant.  Also,  reduction  with  a 
gas  already  containing  a  high  concentration  of  carbon  dioxide  is 
relatively  inefficient. 

Jaubert,  in  French  practice,  attempts  economy  of  reducing 
agent  in  multiple  retort  practice  by  working  at  a  lower  tempera- 
ture. The  practical  effect  of  this  is  two-fold.  A  larger  propor- 
tion of  carbon  monoxide  relative  to  hydrogen  in  the  water-gas 
is  consumed.  This  is  in  accord  with  the  equilibrium  in  the  water- 
gas  reaction: 

CO  +  H20  =  C02  +  H2. 

The  equilibrium  constant, 

_PCO 
" 


decreases  with  decreasing  temperature  (see  page  61).  In  other 
words,  carbon  monoxide  and  steam  concentration  in  the  spent 
water  gas  decrease,  while  carbon  dioxide  and  hydrogen  concen- 
trations increase,  the  lower  the  reaction  temperature.  This  greater 


58  INDUSTRIAL  HYDROGEN 

utilisation  of  the  carbon  monoxide  means  an  increased  positive 
thermal  effect  in  the  reduction  process.  At  the  same  time,  lower 
retort  heats  mean  lower  losses  by  radiation  and  less  heat  con- 
sumed in  raising  gas  and  steam  to  reaction  temperatures.  The 
lower  limit  to  which  this  can  be  carried  is  governed  by  the  re- 
activity of  the  contact  mass.  As  the  temperature  decreases, 
reactivity,  and  therefore  output  per  unit  of  contact  mass,  also 
falls. 

That  attention  is  being  directed  in  technical  practice  to  a 
better  utilisation  of  the  spent  water-gas  is  evidenced  by  a  re- 
cent series  of  patents.  R.  and  J.  Dempster,  Ltd.,32  of  England, 
claim  the  use  of  spent  water-gas  for  the  earlier  part  of  the  re- 
ducing phase.  Fresh  reducing  gas  is  then  passed  through  the  re- 
torts for  the  completion  of  the  reduction  and  is  then  either 
passed  away  or  conditioned  for  use  in  the  earlier  part  of  the  re- 
duction phase.  The  conditioning  provided  appears  to  be  the 
removal  of  steam.  A  later  patent 33  provides  a  method  of  control 
of  waste  gases  burned,  whereby  the  volume  of  the  outgoing  waste 
gases  is  restricted  during  the  exothermic,  oxidising  or  steaming 
phase  and  the  maximum  heating  effect  of  the  gases  is  obtained 
during  the  reducing  phase.  The  controlling  device  is  operated 
in  connection  with  the  hydrogen  valve. 

Harger  and  Lever  Bros.,  Ltd.,34  utilise  the  spent  gas  obtained 
after  reduction  of  the  iron  oxide  by  passing  it  over  copper  oxide 
arranged  adjacent  to  the  iron.  The  heat  of  the  reactions 

CuO  +  H2  =  Cu  +  H20  +  20,300  calories 
CuO  +  CO  =  Cu  +  C02  +  31,700  calories 

is  applied  to  heat  the  iron  material.  The  usual  steaming  phase 
is  then  carried  out  and  the  hydrogen  collected.  This  is  followed 
by  an  air  blast  which  serves  to  reoxidise  the  copper  to  copper 
oxide  and  by  means  of  the  heat  of  reaction 

2Cu  +  02  =  2CuO  +  75,400  calories 

supplies  additional  heat  to  the  reaction  system.  The  carbon  di- 
oxide, hydrogen  and  nitrogen  produced  in  the  three  successive 
stages  of  the  process,  reduction,  steaming  and  air  blast,  may  be 
separately  collected.  Owing  to  the  exothermic  nature  of  the  ad- 

82  B.  P.  126,251/1918  and  126,256/1918. 

83  B.   P.   131,347/1918. 
"B.  P.  131,684/1918. 


HYDROGEN  FROM  STEAM  59 

ditional  reactions  in  this  system  it  is  to  be  anticipated  that  ex- 
ternal heating  of  any  kind  would  be  unnecessary.  The  ratio  of 
water-gas  consumed  to  hydrogen  produced  could,  in  such  case,  be 
kept  down  to  that  required  by  the  equilibrium  data  for  the  sev- 
eral gases  in  contact  with  iron  and  the  iron  oxides,  whereas,  in 
many  installations  now  working,  this  ratio  is  greatly  exceeded. 

The  British  Oxygen  Co.,  Balfour  and  Bray  35  contemplate  the 
use  of  spent  water-gas  after  an  even  more  thorough  purification 
than  claimed  in  the  Dempster  patents  just  cited.  The  spent 
water-gas  before  re-employment  is  to  be  freed  from  steam,  car- 
bon dioxide  and  sulphur  compounds,  and  then  used  in  the  retorts 
for  reduction  purposes. 

The  data  already  given  enable  one  to  determine  the  relative 
calorific  values  of  the  hydrogen  into  the  holder  and  of  the  water- 
gas  consumed.  This  figure,  which  is  of  importance  when  hydro- 
gen is  to  be  put  to  use  as  fuel  is,  however,  of  secondary  impor- 
tance in  processes  in  which  the  hydrogen  is  used  as  a  hydro- 
genation  agent.  From  the  calorific  data  and  volume  relation- 
ships already  given  it  follows  that  the  calorific  efficiency  of  hy- 
drogen produced  to  water-gas  consumed  is 

0.9  X  55  X  116,000  X  100 

=  49.8  per  cent. 

50  X  116,000  +  42  X  136,000 

"B.  P.  144,751/1919. 


Chapter  III. 
Hydrogen  From  Water-Gas  and  Steam. 

Theoretical. — In  the  water-gas  generator,  in  addition  to  hy- 
drogen and  carbon  monoxide,  a  small  proportion  of  carbon  diox- 
ide is  normally  produced  and,  as  is  well  known,  the  percentage  of 
carbon  dioxide  increases  the  lower  the  temperature  of  the  fuel  bed. 
Examination  shows  that  this  carbon  dioxide  is  most  probably  pro- 
duced from  the  carbon  monoxide  formed  in  the  initial  reaction 

C  +  H20  =  CO  +  H2 

by  further  interaction  of  the  gas  with  steam  according  to  the 
so-called  water-gas  reaction: 

CO  +  H20  =  C02  +  H2. 

This  reaction  is  in  reality  an  equilibrium  process,  the  direction 
of  the  reaction  being  governed  by  the  temperatures  maintained 
and  the  concentrations  of  the  respective  components.  The  ve- 
locity with  which  the  reaction  occurs  is  largely  determined  by 
the  nature  of  the  solid  material  in  contact  with  which  the  reac- 
tion is  carried  out.  A  number  of  substances  accelerate  the  veloc- 
ity of  reaction  by  acting  as  catalytic  agents.  In  the  fuel  bed  of 
the  water-gas  generator  it  is  probably  the  mineral  constituents 
forming  the  ash  of  the  coke  employed  which  assist  in  the  pro- 
motion of  the  water-gas  reaction.1  Actual  experimental  deter- 
minations of  the  equilibrium  in  a  range  of  temperatures  extend- 
ing from  686°  C.  to  1,100°  C.  made  by  Hahn  have  permitted 
the  deduction  of  an  equation  2  representing  the  variation  of  the 
equilibrium  position  with  temperature.  By  means  of  the  equa- 
tion 

PCOXPH20          2116 
log  K  =  log  -  -  — +  0.783  log  T  -  0.00043  T 

PC02  XPH2 

1  See  Gwosdz,  Z.  angew.  Chem.  1918,  1,  137. 

ZZ.  physik.  Chem.  1902,  1,2,  705;  1903,  hk,  513;  1904,  W,  735. 

60 


HYDROGEN  FROM  WATER-GAS  AND  STEAM      61 

the  following  table  of  values,  extrapolated  below  700°  C.  but 
fitting  the  experimental  data  from  that  temperature  onwards, 
has  been  compiled. 
T°  C.  400°     500°     600°     700°     800°     900°     1,000° 


POO  o 

K  =  _  —  0.05     0.15     0.32     0.58     0.90     1.25      1.62 


At  the  high  temperature  of  the  water-gas  generator,  since  the 
concentration  of  steam  will  simultaneously  be  low,  it  is  obvious 
that  the  concentration  of  carbon  monoxide  will  considerably  ex- 
ceed that  of  carbon  dioxide.  This  is  confirmed  by  the  following 
typical  analysis  of  a  water  gas: 

Hydrogen    ..................  47.1  per  cent 

Carbon  monoxide  ...........  42.6 

Carbon  dioxide  ..............  3.1 

Nitrogen   ...................  3.5 

Methane  ...................  0.4 

Sulphur  compounds  ..........  0.2 

Water  vapor  ................  3.0 

Also,  it  is  evident  that,  at  lower  temperatures,  especially  if  steam 
be  present  in  excess,  the  production  of  carbon  dioxide  with  simul- 
taneous formation  of  hydrogen  is  favored.  It  is  such  conditions 
which  are  maintained  in  methods  of  hydrogen  production  by 
water-gas  catalytic  processes. 

As  the  temperature  is  decreased,  the  rate  at  which  reaction 
occurs  is  diminished.  Consequently,  in  practice,  a  lower  limit  of 
operating  temperature  will  be  set,  below  which  the  attainment 
of  equilibrium  conditions  is  impracticably  slow.  The  limit  of 
temperature  will  be  lower  the  more  efficient  the  agency  employed 
to  assist  reaction  catalytically,  after  the  manner  of  the  ash  con- 
tent of  the  coke.  Assuming  a  catalyst  which  enables  the  re- 
action to  proceed  at  a  sufficient  speed  at  500°  C.  and  a  ratio 
of  steam  to  hydrogen  in  the  exit  gases  of  2  :  1  it  follows  from 
the  equilibrium  data  that  the  ratio  of  carbon  monoxide  to  car- 
bon dioxide  will  be  given  by  the  equation 


"K"      °  — 

•"-^500      


PCO      PH20 
PC02 


62  INDUSTRIAL  HYDROGEN 

PCO        2 
or  0.15= XT 

PC02       l 

PCO 

whence  =  0.07 

PC02 

In  other  words,  carbon  monoxide  will  be  present  in  the  exit  gases 
to  the  extent  of  7/100ths  of  the  carbon  dioxide  content.  In  this 
way,  water-gas  relatively  rich  in  carbon  monoxide  and  poor  in 
carbon  dioxide  may  be  converted  to  a  gas  poor  in  carbon  mon- 
oxide and  rich  in  carbon  dioxide.  And  since,  simultaneously 
with  the  formation  of  carbon  dioxide,  hydrogen  is  produced,  the 
exit  gases  from  an  equilibrium  reaction  at  500°  C.  will  be  rela- 
tively rich  in  hydrogen.  This  is  the  fundamental  basis  of  the 
water-gas  catalytic  process  as  established  technically  by  the 
Badische  Co.  as  a  method  of  preparation  of  cheap  hydrogen  for 
ammonia  synthesis. 

Theoretically,  it  is  possible  still  further  to  depress  the  car- 
bon monoxide  concentration  in  the  exit  gases  from  the  water- 
gas  reaction.  From  the  expression  for  the  equilibrium  constant 

_  PCO  x  PH20 
PC02  X  PH2 

it  is  evident  that  if,  at  any  given  temperature  of  reaction,  means 
be  adopted  to  diminish  the  concentration  of  either  the  carbon 
dioxide  or  hydrogen  resulting  from  the  change,  the  effect  of  this 
will  be  still  further  to  diminish  the  concentrations  of  the  reacting 
carbon  monoxide  and  steam.  Now  it  is  not  desirable  to  withdraw 
hydrogen  as  formed  since  this  is  the  product  desired.  But,  if 
the  carbon  dioxide  concentration  be  maintained  as  low  as  pos- 
sible, the  percentage  of  carbon  monoxide  will  be  correspondingly 
lowered.  A  ready  means  of  keeping  the  carbon  dioxide  concen- 
tration low  is  at  hand  in  the  utilisation  of  the  fact  that  lime  will 
absorb  carbon  dioxide  readily  from  moist  gases  even  at  500°  C. 
to  form  calcium  carbonate.  Absorption  by  lime  continues  until 
equilibrium  is  set  up,  at  the  given  temperature,  in  the  reaction 

CaO  +  C02  =  CaC03. 


HYDROGEN  FROM  WATER-GAS  AND  STEAM      63 

Now,  at  every  temperature,  there  is  a  definite  partial  pressure  of 
carbon  dioxide  in  equilibrium  with  the  lime  and  calcium  car- 
bonate, the  dissociation  pressure  of  calcium  carbonate.  This  has 
been  accurately  determined  by  Johnston3  and  has  been  shown 
to  give  the  following  values  over  the  range  of  temperatures  here 
in  question: 

T°  C.  587    605    631     671      680    691     711 

pco  1.0    2.3    4.0     13.5     15.8     19.0    32.7  mm. 

Therefore,  so  long  as  the  water-gas  reaction  be  conducted  at 
587°  C.  in  the  presence  of  an  excess  of  lime  the  maximum  partial 
pressure  of  the  carbon  dioxide  which  may  be  present  is  1  mm. 
Hence,  since, 

PCO  XPH20  PCO 

K  =  — or     =  K 

PC02  X  PH2  PC02 

it  follows  that  by  repressing  in  this  manner  the  carbon  dioxide 
concentration  from  a  concentration  of  about  13  per  cent,  which  it 
would  have  in  the  exit  steam-gas  mixture  of  the  simple  continuous 
catalytic  process  already  discussed,  to  a  partial  pressure  of  1  mm. 
or  approximately  0.13  per  cent  in  presence  of  lime,  the  carbon 
monoxide  can  be  depressed  in  the  like  ratio.  The  theory  of  con- 
ducting the  water-gas  reaction  in  presence  of  lime  is  the  basis  for 
the  patented  process  of  the  Griesheim-Elektron  Company,  which 
forms  the  second  method  of  hydrogen  production  from  water-gas 
and  steam  which  will  receive  consideration. 

The  proposals  embodied  in  a  series  of  patents  obtained  by 
Dieffenbach  and  Moldenhauer  represent  an  attempt  at  a  simpli- 
fied mode  of  operation  of  both  these  methods  of  hydrogen  produc- 
tion. The  simplification  attempted  lies  in  the  effort  both  to  pro- 
duce water-gas  and  to  throw  the  water-gas  equilibrium  over  to  the 
carbon  dioxide-hydrogen  side  in  a  onestage  process.  By  suitable 
treatment  of  the  carbon  it  is  sought  to  increase  its  activity 
towards  steam  and  at  the  same  time  to  increase  the  reaction  ve- 
locity of  the  water-gas  reaction  in  the  presence  of  carbon  dioxide 
absorption  agents  to  such  an  extent  that  hydrogen  and  carbon 
dioxide,  substantially  free  from  carbon  monoxide,  leave  the  fuel 

*J.  Am,  Chem.  Soc.t  1910,  32,  938. 


64  INDUSTRIAL  HYDROGEN 

bed.  The  details  of  such  proposals  will  be  discussed  in  the  last 
section  of  the  chapter. 

The  Continuous  Water-Gas  Catalytic  Process 

Outline  of  the  Process. — Water-gas  and  steam  are  admixed, 
raised  to  a  temperature  of  approximately  450°  C.  by  means  of 
heat  exchangers,  and  are  passed  over  a  suitable  catalytic  agent. 
The  water-gas  reaction  is  brought  about  as  represented  by  the 
equation : 

H2  +  CO  +  H20  (excess)  =  2H2  +  C02  +  excess  steam. 

Water  Gas 

The  sensible  heat  of  the  gases  leaving  the  catalytic  agent  is  given 
up  to  fresh  incoming  gases  in  the  heat  exchangers  and  the  gas  is 
then  freed  from  steam  in  condensers.  The  resulting  mixture  con- 
tains about  2-3  per  cent  of  carbon  monoxide  (dry  basis) ,  the  resi- 
due consisting  mainly  of  hydrogen  and  carbon  dioxide  approxi- 
mately in  the  ratio  of  2:  1.  In  the  succeeding  operation,  the  car- 
bon dioxide  (30-35  per  cent)  and  sulphuretted  hydrogen  are  re- 
moved, generally  by  washing  with  water  under  a  working  pres- 
sure of  15-40  atmospheres.  The  residual  gas,  containing  approxi- 
mately 95  per  cent  hydrogen,  3  per  cent  of  carbon  monoxide, 
residual  nitrogen  and  methane,  may  be  used  as  such  in  certain 
operations  or  may  be  submitted  to  special  purification  processes. 

Catalysts  for  the  Reaction. — A  resume  of  the  patent  litera- 
ture will  serve  to  indicate  the  various  proposals  which  have  been 
made  to  accelerate  the  reaction  between  the  carbon  monoxide  and 
steam. 

Hembert  and  Henry  proposed  the  use  of  fireproof  materials 
at  a  red  heat  to  promote  reaction  between  water-gas  and  excess 
of  steam.  Read  in  B.  P.  3,776/1885  suggested  the  use  of  metallic 
oxides  as  catalysts.  The  patent  granted  to  Mond  and  Langer 
(B.  P.  12,608/1888)  claimed  the  removal  of  carbon  monoxide  and 
hydrocarbons  from  fuel'gases  by  passage  with  excess  of  steam  over 
heated  catalysts,  for  example,  nickel  at  temperature  of  350-400°, 
cobalt  at  400-450°.  The  hydrocarbons  were  said  to  be  decom- 
posed, while  the  carbon  monoxide  was  claimed  to  be  practically 
completely  eliminated.  Ellworthy  suggested  the  use  of  nickel  or 
iron  in  a  similar  manner  with  a  mixture  of  water-gas  and  steam 


HYDROGEN  FROM  WATER-GAS  AND  STEAM      65 

(Fr.  P.  355,324/1905),  while  an  earlier  patent  of  Pullman  and 
Ellworthy  (B.  P.  22,340/1891)  proposed  to  separate  the  carbon 
dioxide  by  processes  of  diffusion  and  of  fractional  solution.  The 
Compagnie  du  Gaz  de  Lyons  (Fr.  P.  375,164/1906)  claimed  the 
use  of  iron  oxide  at  600°.  A  year  later  Vignon  (B.  P.  20,685/ 
1907)  applied  for  a  patent  for  a  process  as  above,  using  iron,  or 
oxides,  or  platinum  at  red  heat,  but  the  application  was  not 
granted.  Ellis  and  Eldred  (U.  S.  P.  854,157/1907)  employed 
nickel,  iron,  or  manganese  for  catalytic  agents,  using  a  specially 
designed  superheated  reaction  chamber.  Naher  and  Miiller  (B.  P. 
20,486/1911)  suggest  the  use  of  a  contact  mass  of  rhodium  or  pal- 
ladium asbestos  at  a  working  temperature  of  800°.  A  product 
containing  less  than  0.4  per  cent  of  carbon  monoxide  is  claimed. 
It  is  obvious  from  the  equilibrium  considerations  already  given 
that,  at  the  temperature  stated,  such  a  low  content  of  carbon 
monoxide  could  only  be  obtained  by  the  use  of  a  prohibitively 
large  excess  of  steam. 

The  technical  development  of  the  process  was  undertaken  by 
the  Badische  Anilin  und  Soda  Fabrik  and  resulted  in  a  series  of 
patents  in  the  interval  from  1912  down  to  the  present  time.  It 
will  be  seen  that  several  of  the  claims  put  forward  by  them  are 
clearly  anticipated  in  the  preceding  patents.  Others,  however, 
show  definite  modifications  of  earlier  practice. 

B.  P.  26,770/1912,  or  its  analogue  U.  S.  P.  1,157,669,  calls  for 
the  carrying  out  of  the  process  under  pressures  of  4-40  atmos- 
pheres at  temperatures  between  the  limits  of  300  and  600°,  using 
nickel,  cobalt  or  iron  as  catalysts.  The  increase  in  pressure  fa- 
cilitates both  reaction  velocity  and  heat  exchange.  .The  process  is 
stated  to  be  specially  applicable  to  gases  with  small  carbon  mon- 
oxide content,  though  no  record  is  available  as  to  any  technical 
utilisation  of  the  patent.  A  somewhat  later  patent 4  claims  an 
improvement  for  the  maintenance  of  the  requisite  temperature  in 
the  catalytic  mass  by  the  addition  of  air  or  oxygen.  This  gas 
can  be  admitted  in  sufficient  amount  to  make  the  process  ther- 
mally self-sustaining,  owing  to  the  heat  of  interaction  of  the  oxy- 
gen with  hydrogen.  The  steam  required  for  the  water-gas  re- 
action may  be  supplied  wholly  or  in  part  in  this  manner.  Various 
patents 5  claim  the  use  of  specially  prepared  catalysts  composed 

* B.  P.  27,117/1912  ;  U.  S.  P.  1,200,805. 

•  B.  P.  8,864/1913  ;  27,955/1913 ;  U.  S.  P.  1,114,096 ;  1,113.097  ;  1,115,776. 


66  INDUSTRIAL  HYDROGEN 

of  oxide  of  iron  with  suitable  binding  agents  and  of  nickel  incor- 
porated with  various  support  materials.  The  use  of  catalysts 
containing  nickel  apparently  tends  towards  the  simultaneous  pro- 
duction of  methane  since  B.  P.  27,963/1913  (U.  S.  P.  1,330,772/ 
1920)  deals  with  catalysts  with  which  the  tendency  to  methane 
production  is  minimised  or  suppressed.  The  materials  cited  in 
this  patent  are  numerous  and  the  patent  represents  a  distinct 
departure  from  previous  claims  in  that  the  use  of  one  or  more 
promoters  in  conjunction  with  a  substance  acting  as  basic  catalyst 
is  covered.  The  principal  claims  are  for  iron  oxide  in  admixture 
with  oxides  of  chromium,  thorium,  aluminium,  nickel,  with  other 
mixtures  of  oxides  such  as  those  of  zinc,  lead,  copper,  uranium, 
etc.  A  later  patent6  returns  to  the  earlier  claims  of  B.  P. 
27,955/1913  and  specifies  forms  of  oxide  of  iron  more  rugged  than 
the  materials  earlier  suggested  for  use  in  technical  work.  Oxide, 
hydroxide  and  carbonaceous  iron  ores,  employed  either  in  bulk 
or  brought  into  suitable  form  by  powdering  and  admixture  with 
binding  agents  are  claimed  as  the  catalytic  agents.  The  minerals 
employed  should  preferably  be  low  in  sulphur,  chlorine,  phos- 
phorus and  silicon.  High  temperatures  are  to  be  avoided  in  the 
production  of  such  agents,  a  limit  being  set  at  650°.  Spathic 
iron  ore,  for  example,  when  ignited  below  650°  gives  an  active 
catalyst.  It  is,  however,  friable  and  for  technical  use  would  prob- 
ably require  pulverising  and  briquetting  with  a  suitable  binding 
agent.  The  claims  of  D.  R.  P.  284,176/1914  (U.  S.  P.  1,301,151) 
specify  the  use  of  the  oxides  of  rare  earths,  especially  cerium 
oxide,  not,  as  in  U.  S.  P.  1,330,772,  as  promoters  to  other  oxide 
agencies,  but  as  the  basic  catalyst  with  which  other  activating 
agents  may  be  employed. 

The  specifications  of  the  Badische  Co.  with  respect  to  suit- 
able iron  oxide  ores  exclude  from  use  iron  oxide  obtained  from 
the  roasting  of  pyrites  ores.  The  utilisation  of  this  material  in 
suitable  form  is  the  object  of  the  patent  claims  of  Buchanan 
and  Maxted7  who  protect  the  use  of  oxide  of  iron  ob- 
tained by  lixiviation  of  sodium  ferrite.  Such  material  is  a  by- 
product in  the  causticisation  of  sodium  carbonate  by  the  Loewig 
process,  in  which  roasted  iron  pyrites  is  used  for  calcination  with 
sodium  carbonate  at  elevated  temperatures,  with  production  of 

•B.  P.  16,494/1914. 
*B.  P.  6,476/1914. 


HYDROGEN  FROM  WATER-GAS  AND  STEAM      67 

sodium  ferrite  and  evolution  of  carbon  dioxide.  The  iron  oxide 
obtained  after  lixiviation  of  the  ferrite  is  an  active  agency  for 
the  water-gas  reaction,  the  presence  of  some  undecomposed  ferrite 
probably  acting  as  an  auxiliary  activator.  A  succeeding  patent 8 
to  the  same  applicants  claims  the  use  of  metallic  couples  for  in- 
creased efficiency.  Thus,  by  reduction  of  the  iron  oxide  obtained 
in  the  manner  just  stated  and  by  immersion  of  the  iron  thus  ob- 
tained in  a  solution  of  copper  salts,  a  metallic  couple  is  obtained 
with  which  improved  conversion  at  increased  velocities  is  ob- 
tained. Similarly  an  iron-silver  couple  may  be  utilised. 

No  published  data  are  available  as  to  the  relative  activities 
of  the  many  catalytic  agents  cited  in  this  resume.  Furthermore, 
catalytic  activity  alone  is  no  criterion  of  the  suitability  of  a 
given  substance  or  mixture  for  use  in  the  process.  The  choice 
of  catalyst  is  governed  by  a  variety  of  factors  of  which  catalytic 
activity  is  but  one  of  importance.  The  robustness  of  the  material, 
the  economy  of  its  preparation,  density,  sensitivity  towards 
poisons,  and  to  temperature  change,  are  all  features  of  the  cataly- 
tic agent  which  require  consideration  and,  in  conjunction  with 
catalytic  activity,  determine  the  choice.  The  following  table, 
Rowever,  compiled  from  experimental  investigations  of  the  writer, 
will  serve  to  give  a  degree  of  orientation  in  the  matter  of  the  rela- 
tive activities  of  materials  which  have  been  chosen  as  types  of 
the  catalytic  agents  claimed  in  the  patent  literature  just  de- 
scribed. The  experimental  investigation  was  made  with  a  special 
form  of  water  gas  having  a  carbon  monoxide  content  of  38  per 
cent.9  Small  amounts  of  catalyst  as  specified  in  the  table,  were 
employed.  The  ratio  of  steam  to  hydrogen  was  such  that,  unless 
otherwise  stated,  at  equilibrium  at  500°  C.,  a  ratio  H20:  H2 
=  2:1  was  maintained.  The  speed  of  gas  flow  is  indicated  in 
the  column  headed,  Space  Velocity,  which  represents  the  volume 
of  water-gas  passed  per  hour  per  unit  apparent  volume  of  cat- 
alyst. The  numbers  in  the  first  column  refer  to  the  notes  ap- 
pended to  the  table. 

"B.  P.   6,477/1914. 

8  This  water-gas  was  obtained  from  a  plant  producing  hydrogen  by  the 
liquefaction  process.  A  low  temperature  water-gas  is  produced  rich  in  hydrogen, 
low  in  carbon  monoxide  and  relatively  high  in  carbon  dioxide.  (See  p.  91, 
Chap.  IV.)  The  gas  used  in  the  experiments  under  consideration  had  been 
freed  from  its  carbon  dioxide  content  by  pressure  water  washing  and  treatment 
with  caustic  soda  solution.  The  main  constituents  wereH3=57%;  CO  =  : 


68 


INDUSTRIAL  HYDROGEN 


Catalyst 
No. 

Constituents 

Tem- 
pera- 
ture 

Space 
Velocity 

%C02 

%CO 

1 

Fe-Cr  oxides 

450° 

6500 

24.8 

1.6 

la 

Fe-Cr  oxides 

450 

7000 

24.7 

1.8 

2 

Fe-Cr-Th  oxides 

450 

5000 

25.0 

1.2 

2a 

Fe-Cr-Th  oxides 

500 

9000 

25.2 

1.0 

3 

Fe-Ni-Cr  oxides 

460 

4000 

25.0 

1.2 

4 

Zn-Cr  oxides 

550 

2500 

8.8 

10 

5 

Pb-Ur  oxides 

515 

2000 

24.8 

1.7 

6 

Fe  oxide 

550 

720 

18.0 

10 

(bog  iron  ore) 

7 

Haematite 

580 

1000 

20.0 

— 

8 

Fe  oxide  from  Spathic 

550 

720 

22.3 

4 

ore 

9 

8  with  Cr  oxide 

450 

1600 

24.3 

2.3 

10 

Bauxite 

450 

660 

2.5 

30 

11 

Fe  oxide  ex 

510 

1200 

15.0 

15 

sodium  ferrite 

12 

11  with  Cu  as  couple 

485 

1200 

23.0 

3.0 

NOTES  ON  THE  CATALYSTS 

1.  From  85  parts  ferric  nitrate  and  15  parts  chromium  ni- 
trate precipitated  as  hydroxide  and  ignited  at  500°  C.10 

la.    As  in  1,  but  prepared  by  ignition  of  nitrates  in  stream 
of  air  and  steam  at  500°. 

2.  From  195  parts  ferric  nitrate,  4  parts  ammonium  bichro- 
mate, 1  part  thorium  nitrate.    Solution  evaporated  and  residue 
ignited  at  500°. lx 

2a.    As  in  2,  H20/H2  ratio  =  3:1. 

3.  From  40  parts  ferric  nitrate,  5  parts  nickel  nitrate,  5  parts 
chromium  nitrate.    Solution  precipitated  with  potassium  carbo- 
nate, precipitate  washed,  dried  and  ignited.12 

4.  Ignition  of  zinc  oxide  with  twice  its  weight  of  chromium 
nitrate. 

10  Cf.  B.  P.  27,963/1913.     U.  S.  P.  1,330,772/1920. 

11  Cf.  B.  P.  27,963/1913.     U.  S.  P.  1,330,772/1920. 

12  Cf.  B.   P.   27,963/1913. 


HYDROGEN  FROM  WATER-GAS  AND  STEAM      69 

5.  From  3  parts  of  lead  nitrate  with  one  of  uranium  ni- 
trate. 

6.  From  Dutch  bog  iron  ore,  calcined  in  air  for  2  hours  at 
600°. 

7.  A  coarsely  powdered  sample  of  massive  haematite,  heated 
initially  to  600°. 

8.  From  five  ccs.   of  coarsely  powdered  spathic  iron  ore 
heated  in  a  current  of  water  gas  until  carbon  dioxide  evolution 
ceased. 

9.  The  residue  from  8,  soaked  in  strong  solution  of  chro- 
mium nitrate,  dried  and  ignited. 

10.  A  coarsely  powdered  sample  of  bauxite  with  moderate 
iron  content. 

11.  Iron  oxide  from  sodium  ferrite.13 

12.  Iron  oxide  as  in  11,  reduced  to  metal,  immersed  in  cop- 
per nitrate  until  some  copper  separated,  then  washed,  dried  and 
used.14 

It  is  evident  from  such  experiments  that  catalysts  consisting 
in  the  main  of  iron  oxide,  preferably  with  other  oxides  as  pro- 
moters will  catalyse  the  water-gas  reaction  rapidly  and  effi- 
ciently, since  the  data  given  in  respect  to  the  first  three  catalysts 
represent  approximately  equilibrium  conditions  under  the  con- 
ditions of  experiment  chosen.  The  writer  has  employed  for  large 
scale  trials  iron-chromium  oxide  catalysts  and  iron- chromium- 
cerium  oxide  catalysts  with  complete  success.  They  have  been 
used  with  and  without  the  use  of  binding  agents.  The  velocities 
quoted  above,  however,  are  not  realisable  in  large  scale  work- 
ing. Available  information  seems  to  indicate  that  the  Badische 
Co.  employed  iron-chromium  oxide  catalysts  upon  a  porous  sup- 
port, although  they  have  been  credited  with  the  use  of  a  porous, 
spongy  oxide  obtained  by  reduction  and  oxidation  of  Swedish 
iron  ore.  It  is  probable  that  a  space  velocity  not  exceeding  500 
is  used  in  technical  practice. 

Operational  Details. — Consideration  may  first  be  given  to  the 
ratio  of  steam  to  water-gas  employed.  Assuming  an  exit  gas 
temperature  of  550°  and  a  catalytic  agent  capable  of  producing 
equilibrium  at  the  velocity  of  gas  flow  employed,  it  is  interesting 

»Cf.   B.    P.   6,476/1914. 
"Cf.  B.  P.  6,477/1914. 


70  INDUSTRIAL  HYDROGEN 

to  calculate  the  results  obtained  with  various  steam-water-gas 
ratios.  Let  us  assume,  first  of  all,  equal  volumes  of  hydrogen 
and  steam  in  the  exit  gases.  Then,  since  th  e  equilibrium  constant 
is  approximately  0.2, 

PC02      PH20        PC02 
K  =  0.2  = X  — —  or -2  =  0.2. 

PH2        POO          POO 

The  carbon  monoxide  would  be  approximately  one-fifth  the  per- 
centage of  the  carbon  dioxide.  With  a  concentration  of  the  latter 
equal  to  about  30  per  cent  it  follows  that  the  carbon  monoxide 
would  be  about  6  per  cent.  In  practice,  this  high  residual  con- 
centration of  carbon  monoxide  is  not  permissible  and  so  resort  is 
had  to  an  excess  of  steam  which  by  increasing  the  ratio  pjj  Q/PH 
decreases  the  ratio  Pco/pCO  corresP°ndingly.  Apparently  an 
economic  balance  is  set  up  between  excess  of  steam  required  on 
the  one  hand  and  the  quantity  of  carbon  monoxide  subsequently 
to  be  removed  on  the  other  hand.  Endeavour  is  made  to  reduce 
the  carbon  monoxide  of  the  residual  gas  (dry  basis)  to  less  than 
3  per  cent.  From  the  equilibrium  data  this  involves  the  use  of 
approximately  3  volumes  of  steam  to  one  volume  of  water-gas 
and,  with  a  fresh  active  catalyst  giving  approximately  equilib- 
rium values,  this  ratio  suffices.  As  the  cat  alyst  deteriorates  with 
use,  however,  and  the  attainment  of  equilibrium  conditions  be- 
comes less  easy,  extra  steam  is  added  to  compensate  for  this  loss 
of  activity.  It  is  probably  economical  to  use  a  catalyst  no  longer 
than  the  period  over  which  the  requisite  reduction  of  carbon  mon- 
oxide concentration  can  be  attained  without  using  more  than  5 
volumes  of  steam  to  one  of  water-gas.  For  iron  oxide  catalysts 
of  the  type  named  a  "life"  of  six  months  may  be  assumed.  In 
the  initial  period  of  running,  3  volumes  cf  steam  per  volume  of 
water-gas  will  suffice,  while  towards  the  end,  as  much  as  five 
volumes  will  be  in  use.  It  should  be  observed,  as  perusal  of  the 
equilibrium  equation  shows,  that  elimination  of  carbon  mon- 
oxide to  negligible  quantities  could  only  be  secured  with  pro- 
hibitive excesses  of  steam.  Thus  if  3  volumes  of  steam  reduce 
the  carbon  monoxide  content  to  3  per  cent  at  equilibrium,  it  will 
require  6  volumes  of  steam  to  reduce  the  percentage  to  1.5  per 
cent,  12  volumes  to  reduce  it  to  0.75  per  cent,  and  so  on.  Such 


HYDROGEN  FROM  WATER-GAS  AND  STEAM      71 

quantities  of  steam  are  economically  impossible.  Lowering  the 
temperature  at  which  the  catalyst  was  active  would  assist  some- 
what in  obviating  the  use  of  such  quantities  of  steam  by  lowering 
the  value  of  K. 

As  to  steam  and  water-gas  specifications  the  following  points 
may  be  detailed.  Low  pressure  steam  is  adequate  for  the  process. 
A  part  of  the  requisite  steam  concentration  may  be  obtained  by 
passing  the  water-gas  counter-current  to  a  stream  of  hot  water. 
Exhaust  steam  may  also  be  used.  Steam  at  a  pressure  suffi- 
cient to  operate  an  injector  for  the  water-gas  has  been  employed 
in  order  to  obtain  an  easily  regulated  mixture  of  the  two  con- 
stituents. The  water-gas  employed  should  be  made  from  a  well- 
coked  coal  as  free  as  possible  from  undecomposed  tar  and  hydro- 
carbon-yielding constituents.  Unsaturated  hydrocarbons  retard 
the  velocity  of  the  reaction.  Saturated  hydrocarbons  have  no  in- 
fluence on  the  reaction  velocity  but  represent  inert  constituents 
difficult  to  remove  from  the  residual  hydrogen.  For  the  same 
reason,  unless  the  hydrogen  is  to  be  used  for  ammonia  synthesis, 
the  nitrogen  content  of  the  water-gas  should  be  maintained  as 
low  as  possible,  since  it  is  impossible  to  remove  this  constituent 
in  technical  practice.  In  regard  to  other  impurities,  it  is  only 
necessary  to  remove  mechanical  impurities  siuch  as  coke-dust,  and 
this  is  effected  generally  by  scrubbing  in  a  mechanical  scrubber. 
It  is  not  necessary  to  remove  hydrogen  sulphide  from  the  water- 
gas  before  use,  since,  in  presence  of  the  excess  steam  employed, 
the  sulphide  is  not  fixed  by  the  iron  oxide  catalyst,  but  passes 
on  unaffected  and  may  be  removed  along  with  the  carbon  dioxide 
in  a  subsequent  operation.  Furthermore,  the  organic  sulphur 
compounds  present  in  the  gas  are  catalytically  converted  during 
the  process  to  hydrogen  sulphide  and  carbon  dioxide. 

CS2  +  2H20  =  CO2  +  2H2S 

The  effluent  gases  from  the  catalyst  chamber  are  thus  free  from 
carbon  sulphur  compounds  which,  ordinarily,  are  difficult  to  re- 
move and  frequently  are  troublesome  in  the  uses  to  which  the 
hydrogen  is  put,  as  for  example  in  catalytic  hydrogenation  proc- 
esses. 

The  thermal  effect  of  the  reaction  is  approximately  adequate 
to  make  the  process  self-sustaining.  At  ordinary  temperatures 
the  conversion  involves  the  evolution  of  10,500  calories: 


72         .-  INDUSTRIAL  HYDROGEN 

CO  +  H20  =  C02  +  Ha  +  10,500  cals., 

and  it  may  be  calculated  that,  at  a  temperature  of  500°  the  va- 
riation of  the  heat  of  reaction  with  temperature  reduces  this  quan- 
tity to  9,650  calories.  A  simple  calculation  based  on  the  specific 
heats  and  quantities  of  the  incoming  and  outgoing  gases  serves 
to  show  that  the  heat  of  reaction  is  sufficient  to  raise  the  tem- 
perature of  an  average  reaction  mixture  by  about  70-100°  C. 
Obviously  the  actual  temperature  rise  will  depend  on  the  com- 
position of  the  gas.  If  a  high  steam-water-gas  ratio  is  used 
the  temperature  rise  will  be  correspondingly  low.  Also,  if  a 
semi-water-gas  is  used  in  order  finally  to  obtain  a  nitrogen- 
hydrogen  mixture,  the  thermal  capacity  of  the  nitrogen  content 
will  also  tend  to  diminish  the  temperature  rise.  Since  the  mean 
temperature  interval  through  which  the  gases  must  be  raised  is 
about  450°  C.  it  is  apparent  that  a  heat  exchanger  equipment 
capable  of  giving  an  80  per  cent  heat  regeneration  with  a  tempera- 
ture differential  of  approximately  100°  C.  between  inside  and  out- 
side gases  would  suffice  to  make  the  process  self-sustaining.  As 
the  catalyst  deteriorates  in  efficiency  and  as  correspondingly  more 
steam  is  used,  the  net  increase  in  temperature,  due  to  reaction, 
correspondingly  diminishes.  In  such  case,  additional  heat  might 
be  required.  Provision  should  therefore  be  made  to  supply  this 
heat  from  external  sources.  This  can  readily  be  done  by  using 
only  the  return  tubes  of  a  heat  exchanger  for  the  steam-water- 
gas  mixture,  maintaining  the  exchanger  at  the  desired  tempera- 
ture by  combustion  of  some  fuel-gas  on  the  other  side  of  the 
tubes.  The  gases  leaving  the  exchanger  system  cannot  be  sen- 
sibly lower  than  90°  C.  in  temperature,  since,  otherwise,  consid- 
erable condensation  of  steam  would  occur  in  the  system.  This 
steam  is  removed  by  cooling  in  scrubber  condensers.  Recent  im- 
provements in  the  process  have,  however,  been  directed  towards 
condensation  of  this  steam  and  utilising  the  hot  water  thus  ob- 
tained to  saturate  incoming  gas  with  steam. 

The  removal  of  carbon  dioxide  and  hydrogen  is  the  operation 
immediately  succeeding  the  condensation  of  steam.  The  gases 
are  compressed  to  about  25-30  atms.  and  scrubbed,  counter-cur- 
rent, with  water  under  the  same  pressure.  The  pressure  chosen 
represents  a  compromise  between  several  factors,  including  com- 
pression costs  (which  vary  approximately  as  the  logarithm  of  the 


HYDROGEN  FROM  WATER-GAS  AND  STEAM      73 

pressure),  solubility  of  the  gas  to  be  removed  and  of  the  other 
gases.  In  case  the  gas  is  to  be  used  finally  at  higher  pressures,  it 
may  be  economical  to  conduct  the  water-scrubbing  at  these  higher 
pressures.  In  good  practice,  a  30  per  cent  excess  of  water  over 
that  required  according  to  the  theoretical  solubility  data  for  car- 
bon dioxide,  is  adequate  to  reduce  the  carbon  dioxide  concentra- 
tion from  circa  30  per  cent  to  about  0.1-0.2  per  cent.  At  the  same 
time  the  hydrogen  sulphide  is  reduced  to  negligible  concentrations. 
It  should  be  noted  that  at  increased  pressures  the  solubility  does 
not  increase  at  a  rate  corresponding  closely  to  Henry's  Law.  The 
data  of  Wroblewski 15  show  the  following  solubilities  in  ccs.  per 
cc.  of  water  at  12.4°  C. 

Pressure  in  Atms.  1  5  10  15  20 

Solubility  1.086        5.15        9.65        13.63        17.11 

Losses  of  hydrogen  in  the  process  of  water  washing  are  also 
marked,  actual  practice  showing  a  loss  of  as  much  as  twice  the 
theoretical  loss  of  5  per  cent. 

Modification  of  the  procedure  here  outlined  may  be  introduced 
in  case  the  hydrogen  is  required  for  purposes  of  ammonia  syn- 
thesis. The  alternative  methods  of  operation  aim  at  the  produc- 
tion of  a  nitrogen-hydrogen  mixture  approaching  that  required  in 
the  synthetic  process,  N2  :  H2  =  1  :  3.  This  end  may  be  achieved 
in  several  ways.  Thus,  for  example,  the  water-gas  used  may  be 
modified  by  introduction  of  air  into  the  generator  during  the 
steaming  phase,  in  such  a  proportion  that  the  ratio  of  nitrogen 
to  hydrogen  or  hydrogen-equivalent  gas  (CO)  will,  at  the  con- 
clusion of  the  operations,  yield  a  nitrogen-hydrogen  mixture  of 
the  necessary  volume  relations.  The  same  modification  may  be 
brought  about  by  utilising  a  portion  of  the  "blow"  gases  from 
the  water-gas  generator  along  with  the  water-gas  from  the  "run," 
or  steaming  phase.  By  another  alternative,  the  necessary  nitrogen 
may  be  supplied  in  the  form  of  ordinary  producer  gas.  Finally 
it  is  possible  to  introduce  the  nitrogen  as  air  in  the  catalytic  re- 
action. In  this  case,  a  high  thermal  effect  results  and  care  must 
be  exercised  that  the  temperature  elevation  does  not  become  un- 
duly high,  as,  thereby,  the  conversion  efficiency  would  be  lowered, 
owing  to  the  unfavorable  equilibrium  conditions  in  the  water-gas 
reaction  at  higher  temperatures.  Attention  should  be  directed  to 
the  fact  that,  by  introducing  nitrogen  in  these  several  ways,  inert 

"Compt.  rend.,  1882,  9}f  1,355. 


74 


INDUSTRIAL  HYDROGEN 


constituents  in  the  form  of  the  rare  gases,  argon  and  its  associated 
elements  are  introduced  into  the  gas  mixture.  These  gases  ac- 
cumulate in  a  circulatory  system  of  utilisation  and,  with  methane 
also  present,  compel  the  adoption  of  a  system  of  "blowing  off," 
whereby  a  certain  fraction  of  the  nitrogen-hydrogen  mixture  must 
be  continuously  lost  in  keeping  the  inert  constituents  below  a  per- 
missible maximum  concentration  in  the  operation  of  ammonia 
synthesis. 

Gas  Composition  Flow  Sheets. — The  several  stages  which  have 
just  been  discussed  in  respect  to  operational  details  may  readily 
be  comprehended  from  the  appended  tables  giving  gas  volume  and 
gas  percentage  flow  sheets  for  a  typical  operation  involving  an 
average  blue  water-gas  and  steam  as  reacting  materials.  Assump- 
tion is  made  that  the  equilibrium  conditions  are  such  that  after 
leaving  the  catalyst  chamber  the  gases  contain  2  per  cent  by  vol- 
ume of  carbon  monoxide,  calculated  on  the  dry  gas  basis. 
GAS  VOLUME  FLOW  SHEET 


Stage  of  Operation 

H2 

N2 

CH4 

CO 

C02 

H20 

Total 

Water-gas  

47.1 

3.6 

04 

42.7 

32 

30 

1000 

Steam  added  

471 

36 

04 

42.7 

32 

3030 

400  0 

At  catalyst  exit  

870 

36 

04 

28 

43  1 

263  1 

4000 

After  condenser       .  . 

870 

36 

04 

28 

43  1 

43 

mo 

After    compressor     (30 
atms  )   

870 

36 

04 

28 

431 

0  14 

1370 

After     carbon     dioxide 
scrubber  

803 

325 

04 

25 

02 

01 

867 

GAS  PERCENTAGE  FLOW  SHEET 


Stage  of  Operation 

H2 

N, 

CH4 

CO 

C02 

H20 

Total 
% 

Water-gas  

47.1 

3.6 

0.4 

42.7 

32 

3.0 

100 

Steam  added  

118 

09 

01 

107 

08 

757 

100 

At  catalyst  exit  

21  7 

09 

01 

07 

108 

658 

100 

After  condenser  

61  7 

25 

03 

1.9 

306 

30 

100 

After    compressor     (30 
atms  )   

635 

26 

03 

2.0 

315 

01 

100 

After     carbon     dioxide 
scrubber  

9?,  6 

3.75 

0.45 

2.9 

0.25 

0.1 

100 

* 
HYDROGEN  FROM  WATER-GAS  AND  STEAM      75 

From  the  gas  volume  flow  sheet  it  is  apparent  that  the  ca- 
pacity of  the  catalyst  unit,  exchanger  and  condenser  system  must 
be  quadruple  the  capacity  of  the  plant  generating  water-gas, 
owing  to  the  excess  of  steam  added.  It  will  be  noted  that  the 
carbon  dioxide  scrubber  also  effects  the  removal  of  some  of  the 
other  gases,  losses  in  this  respect  being  both  mechanical  and  due 
to  solution.  Only  in  the  case  of  hydrogen  is  the  loss  serious,  and 
here  it  approximates  to  10  per  cent  of  the  useful  product  desired. 
It  will  be  noted  that  this  loss  accounts  mainly  for  the  diminution 
in  gas  volume  by  conduct  of  the  process.  Thus,  from  100  volumes 
of  water  gas  only  86.7  volumes  of  the  product  result  containing 
80.3  volumes  of  hydrogen.  This  would  be  diminished  to  84.2 
volumes  of  total  gas  were  the  carbon  monoxide  eliminated. 
Nevertheless,  it  is  obvious  that  not  more  than  100/80.3  =  1.25 
volumes  of  water-gas  are  required  in  this  process  to  produce  one 
volume  of  hydrogen  in  the  product  indicated  as  to  purity  by  the 
last  line  in  the  gas  percentage  flow  sheet.  This  is  one  of  the  main 
reasons  for  the  economy  of  the  process  as  contrasted  with  those 
methods  previously  discussed. 

Comparison  of  the  resulting  gas  mixture  with  the  product 
from  the  liquefaction  process,  Chapter  IV,  shows  a  similar  con- 
centration of  carbon  monoxide  but  a  higher  concentration  of  both 
nitrogen  and  methane.  The  former  of  these  two  gases  cannot 
readily  be  removed  and  so  should  be  diminished  in  the  original 
water-gas  if  a  low  concentration  of  impurities  is  desired.  Accord- 
ing to  some  authorities,  the  methane  concentration  is  altered  in 
the  water-gas  catalysis  by  operation  of  one  or  other  of  the  equil- 
ibria : 

CO   +  3H2  =  CH4  +  H20 

C02  +  4H2  =  CH4  +  2H2O 

2CO  +  2H2  =  CH4  +  C02 

It  is  asserted  that,  from  an  original  gas  containing  no  methane,  or 
from  one  with  as  much  as  10  per  cent  methane,  the  issuing  gas 
from  the  catalyst  contains  approximately  0.5  per  cent  of  this  gas 
reckoned  on  the  dry  basis,  free  from  carbon  dioxide.  Confirma- 
tion of  this  point  would  be  of  great  importance,  since  it  would 
enable  the  use  of  cheaper  starting  raw  material  than  water-gas, 
for  example,  coke  oven  gas  or  producer  gas.  Preliminary  experi- 
ments by  the  writer  have  failed  to  confirm  this  view  but  the  mat- 


76  INDUSTRIAL  HYDROGEN 

ter  is  deserving  of  the  closest  investigation.  It  may  be  said,  in 
support  of  the  claim,  that  calculations  on  these  three  equilibria, 
using  the  Nernst  approximation  formula,  indicate  methane  con- 
centrations of  the  order  claimed,  at  500°  C. 

Plant  Details. — A  diagrammatic  flow  sheet  of  the  process  as 
outlined  in  the  gas  composition  flow  sheet  is  given  in  the  accom- 
panying diagram,  Fig.  VI.  The  items  of  this  system  which  call 
for  special  treatment  may  now  be  discussed. 


OUTLET    fon     BUANCQ    GAS 
WHEN    3TAKT/NG    RCACT/ON 


OUTLET  f-Qfi.    WATCR    PLUS    CARBON    D/OX/OE 


FIG.  VI.     Diagrammatic  Flow-Sheet  of  Continuous  Water-Oas  Catalytic  Process. 

(a)  The  Catalyst  Unit. — This  consists  essentially  of  an  iron 
box  to  hold  the  catalyst  material  and  devised  to  ensure  an  even 
distribution  of  the  reacting  gases  and  suitable  thermal  equilib- 
rium. The  original  technical  units  of  the  Badische  Co.  had  a 
capacity  of  25,000  cubic  feet  of  water-gas  per  hour  but  the  later 
installations  were  capable  of  receiving  up  to  35,000  cubic  feet 
per  hour.  The  apparent  volume  of  catalyst  required  for  this 


HYDROGEN  FROM  WATER-GAS  AND  STEAM      77 

latter  output  should  not  be  more  than  75  cubic  feet  with  a  cata- 
lyst of  average  efficiency.  The  mode  of  distribution  of  the 
catalyst  varies  in  different  plants.  In  one  form  the  catalyst  is 
contained  in  a  single  circular  bed  the  diameter  of  which  is  much 
greater  than  the  depth.  Apparently  the  Badische  Co.  adopted 
a  tray  form  of  converter  similar  to  the  familiar  Grillo  contact 
sulphuric  acid  process  converter.  The  catalyst  is  distributed  on  a 
succession  of  trays  separated  from  each  other  by  gas  spaces.  The 
advantages  of  this  type  are  several.  A  friable  catalyst  may  be 
used,  since  the  weight  the  bottom  layers  have  to  support  is  mini- 
mised when  the  material  is  divided  into  several  portions.  Fur- 
thermore, "hot-spots"  and  "short-circuits"  in  the  catalyst  bed  are 
less  serious  in  the  tray  form  of  converter,  since,  between  each  tray, 
the  gas  molecules  have  opportunity  to  come  to  temperature 
equilibrium  before  undergoing  further  conversion  in  the  succeed- 
ing tray.  Trays  facilitate  the  work  of  charging  and  discharging 
and  they  render  possible  arrangements  whereby  the  reacting  gas, 
for  example,  in  this  case  the  steam,  may  be  added  in  several 
stages,  enabling  thereby  a  closer  thermal  control  of  the  process. 
Thus,  it  is  possible  to  conceive  of  the  present  operation  being 
conducted  in  two  units.  In  the  first  the  major  portion  of  the  con- 
version would  be  accomplished.  A  further  addition  of  steam  at 
this  stage  would  cool  the  reacting  gases  down  to  a  temperature 
low  enough  to  enable  a  lower  concentration  of  carbon  monox- 
ide to  be  reached  in  the  second  unit  of  the  converter.  With  a 
multiple  unit  converter  a  varied  sequence  of  units  could  be  ob- 
tained so  arranged  that  the  last  stages  of  the  conversion  were 
always  effected  by  the  most  active  catalyst.  Since  heat  must  be 
conserved  if  the  process  is  to  be  thermally  self-sustaining,  the 
units  should  all  be  heavily  lagged  with  inside  protection  also, 
against  heat  loss,  if  possible.  Fig.  VII 16  represents  diagrammati- 
cally  such  a  scheme,  with  multiple  heat  exchange. 

(b)  Heat  Inter  changers. — The  design  of  the  heat  exchange 
plant  is  of  great  importance  since  the  full  economy  of  the  process 
rests  on  the  self  sustaining  feature  of  the  process  in  regard  to 
heat  and  since,  also,  the  cost  of  the  necessary  equipment  is  a 
considerable  fraction  of  total  plant  cost.  It  will  be  useful  there- 
fore to  emphasize  some  of  the  factors  to  be  observed  in  inter- 

18  Courtesy  of  Chemical  and  Metallurgical  Engineering:  Description  of 
Synthetic  Ammonia  plant,  Oppau,  Germany,  1921,  2k,  391. 


78 


INDUSTRIAL  HYDROGEN 


changer  design.  The  rate  of  transfer  is  relatively  independent  of 
the  thermal  conductivity  of  the  metal  tube  across  which  heat  is 
being  carried.  Transfer  is  poor  if  the  gas  be  flowing  with  stream- 
line motion  since  it  can  only  occur  by  conduction  from  layer  to 


FlQ.   VIIA. 


layer  of  the  poorly  conducting  gas.  Furthermore,  the  stationary 
layer  of  gas  on  the  walls  of  the  tube  offers  a  comparatively  high 
thermal  resistance.  If  the  gas  flow  exceed  the  critical  velocity 
and  the  motion  be  turbulent,  transfer  of  heat  is  much  more  ef- 


FlG.    VIlB. 


ficient.  Also,  the  faster  the  linear  velocity  of  flow  the  thinner 
is  the  stagnant  layer  of  gas  and  so,  the  better  the  heat  transfer. 
The  heat  transfer  in  calories  per  unit  area  per  degree  temperature 
difference  per  hour  may  be  designated  as  the  coefficient  of  heat 


HYDROGEN  FROM  WATER-GAS  AND  STEAM      79 

transfer.    This  coefficient  is  dependent  also  on  the  diameter  of 
the  tube,  falling  off  slowly  with  increase  in  diameter. 

The  economical  size  of  a  heat  interchanger  unit  has  yet  to  be 
determined.  For  the  catalyst  chamber  of  35,000  cubic  feet  ca- 
pacity adopted  by  the  Badische  Co.  the  writer  would  sug- 
gest that  a  unit  containing  not  less  than  1,000  square  feet  of 
interchanger  surface  would  be  a  suitable  unit.  From  some  avail- 
able small  scale  data  it  would  seem  that  at  least  five  such  units 
would  be  necessary  for  the  total  capacity  of  35,000  cubic  feet  per 
hour.  The  size  of  tube  in  the  interchanger  and  their  distribution 
would  be  set  by  the  linear  velocity  of  gas  flow.  This  should  be 
such  that  a  linear  velocity  of  flow  of  not  less  than  30  feet  per 
second  should  be  attained  in  the  coolest  portion  of  the  heat  inter- 
changer system.  The  volume  of  gas  space  inside  and  outside  the 
interchanger  tubes  should  be  approximately  the  same,  a  slightly 
larger  volume  being  permissible,  however,  on  the  side  taken  by 
the  return  gases,  since  these  are  at  the  higher  temperature. 

Condensers. — These  are  usually  of  the  scrubber  type  with 
water  flowing  over  coke  or  some  similar  baffling  material,  counter 
current  to  the  gas  to  be  freed  from  steam.  A  tubular  type  of 
condenser  is,  however,  applicable,  in  which  case  the  condensed 
water  may  be  used  as  feed  water  for  the  boiler  unit  or  to  supply 
to  the  incoming  water-gas  a  portion  of  its  steam  requirements. 
The  hot  water  from  the  scrubber  condensers  may  also  be  used 
for  this  purpose. 

Gas  Compressor. — For  compression  of  the  gas  to  25-30  atmos- 
pheres, double  line  three  stage  compressors  have  been  found  to 
be  eminently  suitable. 

Water  Compressor. — This  is  usually  a  simple  hydraulic  pump 
delivering  water  against  the  given  pressure  of  25-30  atmospheres. 
It  may  be  driven  from  a  motor  or  the  power  requisite  may  be 
supplied  in  part  from  a  Pelton  wheel  operated  by  means  of  the 
exit  water  from  the  pressure  water  scrubbers  and  in  part  from 
an  auxiliary  motor.  Special  attention  must  be  paid  in  the  case 
of  the  Pelton  wheel  to  the  question  of  attack  from  the  water  leav- 
ing the  scrubbers,  since,  owing  to  the  high  concentration  of  dis- 
solved carbon  dioxide,  the  water  has  a  vigorous  corroding  effect 
on  iron. 


80         ;  INDUSTRIAL  HYDROGEN 

Scrubbers  for  Pressure  Water  Washing. — These  are  built  of 
cast  steel  in  order  to  withstand  the  prevailing  pressure.  In  the 
Badische  plant  the  scrubbers  are  tall  narrow  towers  approxi- 
mately 1  meter  diameter  by  12  meters  high,  closely  packed  with 
Raschig  rings  or  similar  packing  material.  A  better  water  distri- 
bution is  obtained  with  this  tall  type  of  scrubber.  Low  efficiency 
was  attained  in  one  plant  where  this  system  of  carbon  dioxide 
removal  was  in  use  with  a  scrubber  in  which  the  ratio  of  height 
to  diameter  was  only  4:1.  Earthenware  packing  is  preferable 
to  iron  packing,  since  the  latter  is  attacked  by  the  carbonated 
water  produced  in  the  process.  The  size  of  the  tower  should  be 
such  that  a  time  of  contact  between  compressed  gas  and  water 
in  a  well-packed  tower  should  be  about  15  minutes  at  a  working 
pressure  of  25  atmospheres;  at  higher  pressures,  less  time  will 
suffice. 

Further  Purification  of  the  Exit  Gases. — Reference  to  the  gas 
composition  flow  sheets  will  show  that  the  main  impurities  are 
carbon  monoxide  (2-3%),  nitrogen  (3-4%)  and  methane 
(0-1%),  with  small  quantities  of  carbon  dioxide  and  traces  of 
sulphuretted  hydrogen.  The  two  last  may  be  completely  re- 
moved by  scrubbing  with  alkalis  or  passage  over  lime.  In  the 
case  of  nitrogen  and  methane,  which  are  present  in  the  incoming 
water-gas,  no  satisfactory  methods  of  removing  the  same  have 
been  developed  technically.  The  elimination  of  such  gases  is  a 
problem  to  be  attacked  in  the  original  water-gas  production.17 
A  variety  of  methods  are  possible  for  the  elimination  of  carbon 
monoxide.  These  are  so  varied  and  so  important  that  they  will 
receive  special  treatment  in  a  later  chapter. 

The  Griesheim-Elektron  Process. 

Outline  of  the  Process. — Water-gas  and  steam  are  admixed, 
raised  to  a  temperature  of  approximately  450°,  and  passed  over 
lime  in  presence  or  absence  of  suitable  activators.  The  water- 
gas  reaction  is  brought  about,  carbon  dioxide  is  absorbed  by  the 
lime  and  a  gas  mixture,  consisting  essentially  of  hydrogen,  traces 
of  carbon  monoxide,  excess  of  steam  together  with  the  nitrogen 
and  methane  content  of  the  original  water-gas,  issues  from  the 
reaction  chamber.  The  residual  gas  is  freed  from  steam  and  may 

"See,  in  this  connection,  Harger,  Chemical  Age  (London),  1919,  1. 


HYDROGEN  FROM  WATER-GAS  AND  STEAM      81 

then  be  utilised  as  such  or  submitted  to  further  purification 
processes. 

Literature  Resume. — A  patent  to  the  French  inventor,  Tessie 
du  Motay  18  claims  the  production  of  hydrogen  by  passing  steam 
and  water-gas,  freed  from  sulphur,  over  heated  lime.  The  re- 
moval of  sulphur  is  quite  unnecessary  as  lime  absorbs  hydrogen 
sulphide  and  catalytically  converts  carbon  disulphide  in  presence 
of  steam  to  hydrogen  sulphide  and  carbon  dioxide  both  of  which 
are  fixed  by  lime. 

CS2  +  2H20  =  C02  +  2H2S. 

The  patent  claims  of  the  Griesheim-Elektron  Co.,  (B.  P.  2523/ 
1909;  Ellenberger,  U.  S.  P.  989,955)  amplify  the  original  claim  of 
du  Motay  in  that,  by  addition  to  the  lime,  either  slaked  or  caustic, 
of  5  per  cent  by  weight  of  iron  powder,  which,  however,  would 
certainly  be  converted  during  the  process  to  iron  oxide,  the  re- 
action may  be  greatly  accelerated.  The  patent  claims  point  out 
that  the  reaction  is  exothermic  so  that,  not  only  is  the  process 
thermally  self-sustaining,  but  that  cooling  is  required  in  order 
to  keep  the  temperature  of  the  reaction  mass  at  or  below  500°  C. 
The  thermal  data  relative  to  the  reactions  are  given  in  the  two 
equations : 

H20  +  CO  =  H2  +  C02  +  10,500  cals. 

CaO  +  C02  =  CaC03  +  43,300  cals. 

A  suitable  method  of  conducting  the  process  is  outlined  in  B.  P. 
13,049/1912,  in  which  vertical  towers  containing  lime  in  the  form 
of  lumps  are  suggested.  It  is  pointed  out  that  the  reaction  is 
not  confined  to  the  surface  but  penetrates  to  the  interior  of  the 
material.  Furthermore,  it  is  claimed  that,  with  lumps  of  lime  in 
vertical  towers,  regeneration  of  spent  material  may  be  effected 
in  situ.  The  resistance  of  the  material  to  such  an  alternation  of 
reactions  will  at  once  be  seen  to  be  of  importance.  In  actual 
practice,  it  has  been  found  that  the  tendency  to  disintegration  is 
ve/y  great  and  that  the  lumps  of  lime  rapidly  change  to  a  pow- 
der, this  factor  constituting  an  important  disadvantage  in  the 
process.  A  patent  to  Siedler  and  Henke19  covers  this  same  use 
of  a  tower  of  lime,  the  interval  of  temperature  recorded  being 

»U.   S.  P.  229,339/1880. 
»U.    S.   P.   1,181,264. 
20  U.   S.  P.   1,173,417. 


82  INDUSTRIAL  HYDROGEN 

400°-750°  C.  A  patent  to  Ellis 20  covers  the  same  ground  as  far 
as  the  essentials  of  the  process  are  concerned.  As  regards  mode 
of  conduct  of  the  process,  Ellis  would  operate  with  chute  con- 
veyors sending  the  lime  downwards  through  the  reaction  system 
counter-current  to  an  ascending  supply  of  gas  and  steam.  As 
specification  for  the  lime,  it  is  suggested  that  a  limestone  low  in 
magnesia  should  be  employed.  For  activation,  both  iron  and 
manganese  oxides  are  specified  and  special  directions  as  to  the 
preparation  of  these  oxides  are  included. 

Mechanism  of  the  Reaction. — The  reaction  has  been  the  sub- 
ject of  extended  experimental  investigation.  Merz  and  Weith  21 
showed  that  carbon  monoxide  when  passed  over  calcium  hydrox- 
ide yielded  hydrogen  with  only  a  small  content  of  carbon  mon- 
oxide at  reaction  temperatures  below  visible  redness.  Engels 22 
investigated  fully  the  influence  of  temperature,  steam  concentra- 
tion, catalyst  additions  and  velocity  of  gas  flow  in  the  same 
reaction.  According  to  Engels,  the  reactions  in  presence  and 
absence  of  a  catalyst  are  different.  When  catalysts  are  absent,  the 
reaction  is  essentially  a  solid-gas  reaction  in  which  the  reacting 
materials  are  calcium  hydroxide  and  carbon  monoxide. 

Ca(OH)2  +  CO  =  CaC03  +  H2. 

The  later  researches  of  Levi  and  Piva  23  indicate  that  this  reac- 
tion proceeds  through  the  intermediate  stages  of  formate  and 
oxalate.  In  support  of  this,  the  interaction  of  sodium  formate 
and  carbon  monoxide  to  form  hydrogen  and  carbon  dioxide  is 
instanced.  Subsequent  investigations  by  the  same  authors 24 
led  to  the  conclusion  that  slaked  lime  could  take  part  in  the 
sodium  formate  reaction  to  the  extent  of  lowering  the  decompo- 
sition temperature  from  375°  C.  to  260°  C.  Experiments  of  the 
writer  have  shown  that  decomposition  of  pure  sodium  formate 
occurs  with  low  velocity  at  260°  C.,  so  that  the  influence  of  the 
lime  is  probably  to  accelerate  the  velocity  of  decomposition. 
Carbon  monoxide  and  pure  lime  interact  below  300°  C.  to  give 
formate.  Above  this  temperature  calcium  carbonate  and  hydro- 
gen are  produced.  To  a  small  and  very  minor  extent,  the 

^-Ber.,  1880,  IS,  718. 

»  Dissertation,  Karlsruhe  1911.     J.  Gasbeleucht.  1919,  62,  477  and  493. 

*>J.  Soc.  Ghem.  Ind.  1914,  S3,  310. 

24  J.  Chem.  8oc.,  Abstracts  1916,  110,  ii.  525. 


HYDROGEN  FROM  WATER-GAS  AND  STEAM      83 


gas  reaction  between  steam  and  carbon  monoxide  also  takes 
place  when  pure  lime  alone  is  present. 

In  presence  of  a  catalyst,  however,  such  as  iron  oxide,  Engels 
points  out  that  the  reaction  is  quite  different.  The  main  process 
is  then  the  gas  reaction 

CO  +  H20  =  C02  +  H2 

in  contact  with  the  iron  oxide.  The  slower  reaction  of  carbon 
monoxide  with  calcium  hydroxide  undoubtedly  occurs,  but  it  is 
negligible  in  effect  when  compared  with  the  catalysed  gas  reac- 
tion. The  relative  rapidities  of  the  two  reactions  are  shown  by 
the  following  data  with  regard  to  a  carbon  monoxide — steam 
mixture  containing  19  per  cent  of  the  former,  at  a  working  tem- 
perature of  500°  C.,  the  gas  velocity  being  measured  at  20°  C. 
and  referred  to  1  litre  of  contact  agent. 


Contact  agent 

Velocity 
of  CO  in  litres 
per  hour  per  litre 
of  contact  agent 

CO  con- 
centration 
in  exit  gas 

Calcium  hydroxide 
Calcium  hydroxide  5%  iron 

12.5 
138 

QA% 
0.2% 

The  reaction  velocity  is  increased  tenfold  by  iron  oxide  with 
the  given  gas  mixture.  The  steam  concentration  is  also  a  factor 
of  importance.  In  the  reaction  with  pure  calcium  hydroxide  a 
concentration  of  steam  greater  than  that  necessary  to  maintain 
the  lime  in  the  hydroxide  state  merely  acts  as  a  diluent.  Also, 
since  the  hydroxide  is  the  active  agent  and  since,  at  547°  C.,  the 
decomposition  pressure  of  the  hydroxide  becomes  one  atmosphere 
it  is  not  advisable  to  work  at  higher  temperatures  than  547°  C. 
With  iron  oxide  present  and  the  water-gas  reaction  predominat- 
ing, it  follows  from  the  considerations  advanced  in  the  preceding 
discussion  of  the  continuous  catalytic  process  that  excess  of  steam 
is  favorable  to  diminution  of  the  carbon  monoxide  content.  The 
temperature  too  may  be  as  high  as  is  consistent  with  the  use  of 
lime  as  absorption  agent  for  the  carbon  dioxide  produced  in  the 
water-gas  reaction. 

These  observations  as  to  mechanism  give  point  to  the  recent 
proposal  embodied  in  the  patent  to  Greenwood  (B.  P.  137,340/ 


84  INDUSTRIAL  HYDROGEN 

1918).  According  to  this  patent,  the  production  of  hydrogen 
from  water-gas  and  steam  may  be  effected  by  first  leading  the 
water-gas-steam  mixture  over  iron  oxide  or  preferably  an  active 
catalyst  of  the  type  previously  detailed  (e.  g.,  iron-chromium 
oxides)  to  establish  the  water-gas  equilibrium.  By  passage 
through  a  lime  tower  at  the  same  temperature  the  carbon  dioxide 
present  would  then  be  removed  as  far  as  the  equilibrium  concen- 
tration of  the  gas  in  presence  of  lime  at  the  given  temperature 
would  permit.  A  further  passage  of  the  residual  gas  over  an- 
other iron  contact  mass  could  then  be  undertaken,  with  a  corre- 
spondingly further  diminution  in  the  carbon  monoxide  concentra- 
tion. The  gases  could  then  be  cooled,  the  excess  steam  condensed 
and  the  carbon  dioxide  eliminated  by  any  suitable  means.  This 
is,  therefore,  a  proposal  to  separate  the  two  reactions,  the  water- 
gas  reaction  and  carbon  dioxide  absorption  which  occur  simul- 
taneously in  the  process  of  the  Griesheim-Elektron  Co.  and  to 
make  of  them  successive  reactions  which  could  be  repeated  if 
necessary.  With  a  separated  catalyst  and  absorption  agent  a 
more  efficient  promotion  of  the  water-gas  reaction  can  be 
achieved  with  the  more  active  forms  of  catalyst,  the  activity  of 
which  is  subject  to  diminution  when  submitted  to  the  high  tem- 
peratures necessary  for  regeneration  of  the  spent  lime.  Experi- 
mental test  of  this  view,  undertaken  by  the  author  at  the  sug- 
gestion of  Greenwood,  fully  confirmed  its  accuracy.  Lower  final 
concentrations  of  carbon  monoxide  were  obtained  with  successive 
layers  of  catalyst,  lime  and  catalyst  (Fe-Cr  oxides)  than  with  a 
mixture  of  lime  with  five  per  cent  of  iron  oxide.  Considerably 
higher  velocities  of  gas  passage  were  attainable  for  the  same 
purity  of  product. 

Operating  Details. — In  the  main,  the  considerations  obtain- 
ing in  the  continuous  water-gas  catalytic  process  are  applicable  in 
this  process  also,  so  that  extended  discussion  is  not  necessary.  It 
should  be  observed  however  that,  as  the  total  heat  of  reaction  is 
in  this  case  increased  by  the  heat  of  combination  of  carbon 
dioxide  and  lime,  the  net  heat  effect  of  the  reaction  is  strongly 
exothermic. 

CaO  +  CO  +  H20  =  CaC03  +  H2  +  53,800  calories. 

It  would  therefore  be  necessary  to  operate  a  cooling  system  with 
the  process  in  order  that  the  exit  gas  temperature  should  be  suf- 


HYDROGEN  FROM  WATER-GAS  AND  STEAM      85 

ficiently  low  to  favor  low  carbon  monoxide  concentration.  The 
suggestion  has  been  made  that  this  cooling  should  be  effected  by 
means  of  water  tube  coolers  and  that  the  water  so  heated  be 
utilised  to  raise  steam  for  the  process. 

The  additional  factor  of  importance  in  the  process  is  the 
saturation  capacity  of  the  lime  for  carbon  dioxide.  Experiment 
has  shown  that  with  the  lime  in  the  form  of  a  coarse  powder  half 
the  theoretical  capacity  of  the  lime  for  carbon  dioxide  may  be 
utilised  at  500°  C.  without  sensible  increase  in  the  carbon  monox- 
ide content  of  the  issuing  gas.  On  this  basis  it  can  readily  be 
calculated  that  for  a  gas  such  as  is  treated  in  the  pressure  water 
scrubbers  of  the  continuous  catalytic  process  (see  p.  74)  the 
quantity  of  lime  needed  per  1,000  cubic  feet  of  hydrogen  pro- 
duced is  of  the  order  of  100  Ibs.  It  is  probably  this  factor  of 
high  lime  consumption  and  the  disintegration  of  the  lime  with 
repeated  calcination,  which  constitute  the  main  disadvantages  of 
the  process  and  militate  against  large  technical  operation.  No 
case  of  large  scale  use  of  the  process  can  as  yet  be  recorded.  The 
above  data  show  that  with  a  unit  producing  35,000  cubic  feet  of 
hydrogen  per  hour  a  supplementary  lime  burning  plant  of  42 
tons  capacity  per  day  would  be  required.  For  purposes  of  am- 
monia synthesis  it  is  doubtful  whether  even  the  gas  thus  pro- 
duced would  be  sufficiently  free  from  carbon  monoxide  without 
additional  purification.  The  stated  purity  of  the  gas  product  is 

Hydrogen    95.5-97.5 

Carbon  monoxide 0.0-  0.2 

Methane   0.3-  0.5 

Nitrogen    2.0-  4.0 

The  discontinuity  of  the  process  involved  in  the  alternate  ab- 
sorption of  carbon  dioxide  by  lime  and  subsequent  calcination  of 
calcium  carbonate  doubtless  means  high  labor  charges  as  con- 
trasted with  the  continuity  of  the  pressure-water-washing  process 
followed  in  the  continuous  water-gas  catalytic  process.  Mechan- 
ical troubles  in  the  distribution  of  the  lime,  in  a  form  suitable  for 
absorption,  might  also  be  anticipated.  Offsetting  these  difficul- 
ties, the  operation  may  be  conducted  at  atmospheric  pressures 
but,  for  hydrogen  for  ammonia  synthesis,  compression  of  the  gas 
would  ultimately  be  necessary. 

It  is  possible  that  the  process  might  find  application  in  the 


86  INDUSTRIAL  HYDROGEN 

removal  of  residual  carbon  monoxide  from  gases  produced  by 
other  methods.  With  small  carbon  monoxide  concentrations  the 
technique  of  the  process  should  be  very  much  simpler. 

Dieffenbach  and  Moldenhauer  Process. 

Outline  of  the  Process. — Water-gas  is  produced,  the  water-gas 
reaction  is  effected  and,  in  some  proposed  modifications  of  the 
process,  the  carbon  dioxide  formed  is  absorbed,  in  a  one-stage 
process,  by  the  passage  of  steam  through  a  bed  of  fuel  impreg- 
nated or  intermixed  with  materials  which  tend  to  lower  the 
temperature  of  interaction  of  carbon  and  steam.  In  this  way 
it  is  proposed  to  carry  out  in  a  single  operation  the  several 
reactions  which  are  involved  in  the  two  preceding  processes  of 
hydrogen  production.  The  net  reaction  would  therefore  be: 

C  +  2H20  =  C02  +  2H2. 

Thus  far,  no  technical  application  of  the  process  has  been  re- 
corded nor  does  there  appear  to  be  any  immediate  prospect  of 
such  application. 

Literature  Resume. — An  old  patent  to  Tessie  du  Motay  and 
Marechal 25  calls  for  the  production  of  hydrogen  and  carbon 
dioxide  by  heating  fuel  with  lime  or  caustic  soda.  Anticipating 
the  claims  of  Dieffenbach  and  Moldenhauer  are  the  proposals  of 
Krupp  26  in  which  steam  is  caused  to  interact  with  fuels  impreg- 
nated with  hydrates  or  carbonates.  The  carbon  monoxide  con- 
centration is  thereby  suppressed  and  any  carbon  dioxide  pro- 
duced may  be  removed  by  passing  over  heated  lime.  In  a  series 
of  patents  27  various  materials  are  suggested  by  Dieffenbach  and 
Moldenhauer  to  lower  the  temperature  of  interaction  of  steam 
and  carbon.  Coke  impregnated  or  admixed  with  chlorides,  sul- 
phates or  sulphides  is  said  to  be  sufficiently  reactive  at  600°  C. 
Substituting  a  silicate  as  added  material  a  temperature  interval 
of  550°-750°  C.  is  covered.  The  last  patent  of  the  series  advo- 
cates the  production  of  the  reaction  material  by  pulverising  the 
materials,  grinding  to  intimate  admixture  and  briquetting  the 
powdered  product.  Operating  at  the  low  temperatures  stated  a 
carbon  monoxide  concentration  not  exceeding  a  few  tenths  of  one 

25  B.  P.  2,548/1867. 
Z«B.  P.  8,426/1892. 
«B.  P.  7,718,  7,719,  7,720/1910. 


HYDROGEN  FROM  WATER-GAS  AND  STEAM      87 

per  cent  is  the  extent  of  this  impurity  recorded  as  present  in  the 
resulting  gas.  A  later  patent 28  advocates  the  use  of  lime  in  ad- 
dition to  the  catalytic  agent  to  act  as  absorbent  for  the  carbon 
dioxide  produced  and  consequently  to  lower  also  the  carbon 
monoxide  concentration.  As  an  example  of  such  procedure  the 
use  of  coke,  with  an  impregnation  from  a  10  per  cent  potassium 
carbonate  solution  and  admixture  with  five  times  its  weight  of 
lime,  is  cited,  the  reaction  temperature  being  quoted  as  550°" 
750°  C.  The  Griesheim-Elektron  Co.29  adapt  this  idea  to  a  pro- 
cess operating  under  a  pressure  of  10  atmospheres  with  charcoal 
or  lignite  as  source  of  carbon  and  lime  or  baryta  as  activator. 
With  the  former,  a  region  of  temperature  between  600°  and  800° 
C.  is  suggested.  With  the  more  expensive  baryta  lower  tempera- 
tures are  possible.  The  reaction  may  be  conducted,  as  is  the 
generation  of  water-gas,  with  an  alternate  air  blow  and  steam 
run.  The  net  thermal  effect  is  still  strongly  positive,  in  spite  of 
the  endothermic  nature  of  the  reaction  between  carbon  and 
steam,  owing  to  the  heat  of  formation  of  calcium  carbonate. 

C  +  2H20  =  C02  +  2H2  — 19.6  Kg.  Gals. 
CaO  +  C02  =  CaC03  +  43.3  Kg.  Cals. 

The  steam  run  should  therefore  be  proportionately  much  longer 
in  this  case  than  in  the  case  of  water-gas  production. 

A  patent  obtained  by  Prins 30  specifies  other  catalytic  agents 
for  the  same  reaction.  Two  or  more  catalytic  agents  are  to  be 
employed,  one  or  more  from  each  of  the  two  following  groups 

(a)  oxygen  containing  salts  of  the  alkali  or  alkaline  earth  metals 

(b)  inorganic  oxides  or  hydroxides  which  behave  as  non-volatile 
weak  acids  or  acid  anhydrides,  as,  for  example,  B203,  A1203, 
A12C3.    Oxides  of  iron,  chromium  and  manganese  may  also  be 
incorporated.     These,  doubtless,  are  intended  to  promote  the 
water-gas  reaction  as  in  the  two  processes  previously  discussed. 
The  specified  temperature  interval  is  between  300°  and  600°  C. 
As  an  example  of  a  mixture  operative  at  400° -500°  C.  the  fol- 
lowing is  cited :     Ca3  (P04)  2, 1  part ;  Sand,  2  parts ;  Coke,  20  parts. 

General  Discussion. — No  experimental  data  can,  as  yet,  be 
cited  to  illustrate  the  efficiency  of  such  processes  or  the  possi- 

28  B.  P.   8,734/1910. 
MD.  R.   P.   284,816/1914. 
••B.  P.  128,273/1917. 


88  INDUSTRIAL  HYDROGEN 

bilities  inherent  in  such  for  technical  application.  The  test  of 
their  practicability  will  lie  largely  in  a  determination  of  the  at- 
tainable minimum  of  carbon  monoxide  concentration  under  tech- 
nically feasible  conditions.  The  processes  would  be  of  little 
value  as  alternatives  to  the  two  preceding  processes  unless  the 
concentration  of  carbon  monoxide  obtained  was  equal  to  or  less 
than  two  per  cent,  since,  if  such  a  concentration  were  exceeded, 
new  and,  doubtless,  expensive  methods  of  carbon  monoxide  re- 
moval would  be  necessary. 

The  reactivity  of  the  carbon  is  certainly  a  function  of  the 
nature  of  the  carbonaceous  material  employed  as  well  as  of  the 
catalytic  agents  added.  Hence,  it  is  possible  that  certain  types 
of  carbon  might  find  application  where  coke  would  be  of  little 
use.  The  problem  of  availability  of  such  fuels  would  then  be- 
come important. 

Given  a  technically  feasible  reaction  process,  the  plant  re- 
quired would  be  comparatively  simple  and  inexpensive  consisting 
mainly  of  a  generator  and  of  the  apparatus  necessary  for  the 
preparation  of  the  reaction  material  in  suitable  form.  Pulver- 
isers, mixers  and  briquetting  machines  would  seem  to  be  indicated. 

The  gas,  after  production,  would  require  removal  of  carbon 
dioxide  and  then  of  carbon  monoxide.  It  is  unlikely  that  suf- 
ficient lime  could  be  incorporated  in  the  reaction  mixture  to 
absorb  all  the  carbon  dioxide  produced  whilst  still  retaining  the 
necessary  cheapness  of  materials  used. 

Experiments  conducted  by  H.  A.  Neville  under  the  direc- 
tion of  the  writer  have  yielded  results  of  considerable  interest 
from  the  standpoint  of  mechanism  in  such  a  one-stage  process. 
The  catalytic  effect  of  alkali  carbonates  has  been  shown  to  be 
very  much  more  pronounced  than  that  of  any  of  the  other  con- 
tact agents  named  in  the  literature  resume.  Good  water-gas 
reaction  catalysts,  such  as  iron  oxide,  have  little  or  no  effect  in 
speeding  up  the  interaction  of  steam  with  charcoal.  On  the 
other  hand,  the  catalysts  found  for  such  reaction  with  steam  are 
identical  in  nature  and  effect  with  catalysts  for  the  interaction  of 
carbon  dioxide  and  carbon.  Furthermore,  experiment  has  revealed 
that  carbon  in  presence  of  potassium  and  other  alkali  carbonates 
adsorbs  much  larger  quantities  of  carbon  dioxide,  at  a  tempera- 
ture of  445°  C.,  than  does  the  same  carbon  in  absence  of  the 
alkali  carbonate,  although  this  latter  shows  no  specific  adsorptive 


HYDROGEN  FROM  WATER-GAS  AND  STEAM      89 

capacity  for  carbon  dioxide.  The  reactions  occurring  in  this 
process  are  therefore,  in  all  probability,  to  be  ascribed  to  a  suc- 
cession of  reactions 


(1) 

C 

+ 

H20 

— 

COH 

hH2 

(2) 

CO 

+ 

H2  +  K 

,0  = 

C02   - 

h2H2 

(3) 

C02 

+ 

C 

=n 

2CO 

(4) 

2CO 

+ 

2H20 

5= 

2C02H 

h2H2. 

The  catalyst  apparently  performs  two  functions:  (a)  it  cleans  the 
the  surface  of  the  carbon  from  fixed-oxygen  complexes  31  so  mak- 
ing the  carbon  more  reactive;  (b)  it  catalyses  reaction  (3)  above 
and  so  increases  the  yield  of  carbon  monoxide  which  is  then 
transformed  by  reaction  (4)  into  carbon  dioxide  and  hydrogen. 
A  full  discussion  of  this  problem  will  form  the  subject  of  an 
early  publication  in  the  chemical  literature. 

11  See  Lowry  and  Hulett.  J.  Am.  Chem.  Soo.  1920,  42,  1,408. 


Chapter  IV. 
Hydrogen  Prom  Water-Gas. 

For  purposes  of  ammonia  synthesis  and  for  hydrogenation 
processes,  hydrogen  has  been  produced  technically  by  the  suc- 
cessive removal  of  the  various  other  gaseous  constituents  of  water- 
gas.  Of  the  operations  involved,  the  removal  of  the  carbon 
monoxide  is  the  most  important  and  this  has  been  accomplished 
by  the  physical  method  of  liquefaction.  The  divergence  between 
the  boiling  points  of  hydrogen  and  carbon  monoxide  coupled  with 
the  facilities  now  obtaining  for  the  attainment  of  the  low  temper- 
atures requisite,  render  such  a  process  technically  feasible. 

The  sequence  of  operations,  in  outline,  is  as  follows.  Water- 
gas  as  produced  is  freed  from  dust  and  steam  by  an  efficient 
scrubbing  process.  Hydrogen  sulphide  is  then  removed  by  iron 
oxide  box  treatment  or  by  other  suitable  means.  (See  p.  42.) 
The  gas  is  next  compressed  and  freed  from  carbon  dioxide  and 
traces  of  sulphuretted  hydrogen  by  washing  first  with  water  un- 
der pressure  and  then  with  sodium  hydroxide  solutions.  Water 
vapor  is  next  removed  by  refrigeration  in  an  ammonia  refriger- 
ator system.  Thus  freed  from  the  principal  minor  impurities, 
the  water-gas,  still  under  pressure,  passes  to  the  liquefaction 
system  in  which  the  bulk  of  the  carbon  monoxide  and  nitrogen 
together  with  minimal  quantities  of  carbon-sulphur  compounds 
and  phosphorus  compounds  are  separated  in  the  liquefaction 
process.  The  uncondensed  hydrogen  passes  away  with  small 
amounts  of  uncondensed  nitrogen,  methane  and  carbon  monoxide. 
The  carbon  monoxide  may,  if  so  desired,  be  removed  in  subse- 
quent processes  of  chemical  treatment. 

This  sequence  is  indicated  tabularly  in  the  following  gas 
volume  flow  sheet  of  the  typical  changes  from  water-gas  to  the 
hydrogen  issuing  from  the  liquefaction  plant,  the  operations  be- 
ing conducted  with  the  gases  at  20  atmospheres  pressure. 

An  approximate  idea  of  the  possibilities  of  the  liquefaction 

90 


HYDROGEN  FROM  WATER-GAS 


91 


Operation 

H2 

CO 

C02 

H20 

H2S 

N2, 
etc. 

Total 

Water-Gas   

52 

34 

6  6 

3 

04 

A 

inn 

Iron  oxide  box  treat- 
ment to  remove  H2S 
Compression  to  20  at- 
mospheres .  .  *.  

52 
52 

34 
34 

6.6 
66 

3 

015 

4 
4 

99.6 
%75 

Pressure  Water  Wash- 
ing . 

47 

31 

0.1-0.5 

0.13 

37 

82  13 

Pressure      Caustic 
Scrubbing  

47 

31 

0.13 

37 

81  83 

Ammonia      Refrigera- 
tion at  —  35°  C   .  . 

47 

31 

37 

81  7 

Liquefaction  at  —205° 
C  

(a)    Uncondensed  hy- 
drogen fraction  .... 

40 

075 

035 

41.1 

(b)  Liquid  fraction  .  . 

7 

30.25 

3.35 

406 

process  as  regards  removal  of  carbon  monoxide  and  nitrogen  may 
be  gained  from  an  examination  of  the  accompanying  diagram 
(Fig.  VIII)  of  the  vapor  pressures  of  liquid  carbon  monoxide 
and  nitrogen  at  temperatures  in  the  neighbourhood  of  their  boil- 
ing points.1  It  may  be  seen,  however,  by  comparison  of  the 
typical  analysis  of  the  uncondensed  hydrogen  fraction  just  given, 
with  the  simple  data  of  the  diagram,  that  the  latter  are  not 
adequate  in  themselves  to  enable  an  exact  forecast  to  be  made 
of  the  percentages  of  carbon  monoxide  and  nitrogen  present  in 
the  hydrogen  fraction.  For,  from  the  data  in  the  figure,  the 
nitrogen  vapor  pressure  in  equilibrium  at  a  given  temperature  is 
always  greater  than  that  of  the  carbon  monoxide,  whereas,  in  the 
hydrogen  gas  obtained  in  practice,  the  nitrogen  percentage  is 
never  much  greater  than  one  third  of  the  total  impurity.  A 
complete  knowledge  of  maximum  attainable  separations  at  va- 
rious temperatures  could  not  be  obtained  without  a  special  study 
of  the  gas-liquid  phase  relationships  of  various  mixtures  of 
nitrogen  and  carbon  monoxide.  Furthermore,  the  efficiency  of 

1  Nitrogen    by    Fischer    and    Alt    cited    from    Abegg.    Vol.    III.    3.      Carbon 
monoxide  data  by  Baly  and  Donnan.  J.  Chem.  Soo.  1902,  18,  919. 


92 


INDUSTRIAL  HYDROGEN 


76 


V0>0r  Pressures  of  L/qw/d 


/0Q       200       300       400       500 
Pressure 


600 


700       800 


FIG.   VIII.     Vapor  Pressures  of  Liquid   Nitrogen  and  Carbon  Monoxide. 

separation  of  the  condensed  mists  of  carbon  monoxide  and  nitro- 
gen determine  in  part  the  final  concentrations  of  these  gases  in 
the  hydrogen  obtained.  The  problem  has  a  further  complicating 
factor  in  the  solubility  of  hydrogen  in  the  liquid  mixture.  It  can 
however  be  concluded  from  the  diagram  that  to  get  a  satisfactory 
removal  of  nitrogen  and  carbon  monoxide  the  attainment  of 
temperatures  below  73°  Abs.  is  essential.  The  technical  methods 
by  which  this  is  accomplished  differentiate  the  processes  which 
thus  far  have  been  proposed. 

The  Linde-Frank-Caro  Process.  —  This  process  was  operated 
by  the  Badische  Co.  at  Oppau  in  three  units,  each  of  a  capacity 
of  35,000  cubic  feet  of  hydrogen  per  hour,  as  the  source  of  hy- 
drogen for  ammonia  synthesis  in  the  earliest  stages  of  the  tech- 
nical development  of  the  Haber  process.  A  unit  of  17,000  cubic 
feet  of  hydrogen  per  hour  is  in  use  at  Selby,  Yorkshire,  England, 
by  Messrs.  Ardol,  Ltd.,  for  purposes  of  hydrogen  supply  for  the 
hydrogenation  of  oils.  Similar  plants  are  in  operation  in  Europe. 
So  far  as  is  known,  this  process  has  not  been  attempted  on  a 
technical  scale  for  hydrogen  production  in  this  country. 


HYDROGEN  FROM  WATER-GAS  93 

The  essential  features  of  the  process  are  covered  by  U.  S. 
Patents  727,650;  728,173;  1,020,102;  1,020,103;  1,027,862;  1,027,- 
863.  As  actually  operated,  the  liquefaction  process  is  conducted 
in  three  stages.  The  purified  water-gas,  freed  from  hydrogen 
sulphide,  carbon  dioxide  and  water  vapor  in  the  -manner  already 
indicated  in  outline,  leaves  the  ammonia  refrigeration  system  at 
—  35°  C.  It  is  next  cooled  by  heat  exchange  with  the  uncon- 
densed  hydrogen  fraction  leaving  the  liquefaction  system.  Ordi- 
narily, this  hydrogen  is  still  at  the  working  pressure,  in  the  aver- 
age case,  20  atmospheres.  An  additional  cooling  effect  could  be 
obtained  by  allowing  the  hydrogen  to  expand  to  atmospheric 
pressure  either  with  or  without  the  performance  of  external  work 
before  entering  the  interchanger,  but  this  is  not  done  in  technical 
operation  of  the  Linde  system,  because  of  the  advantage,  in  the 
subsequent  utilisation,  of  having  a  compressed  gas.  The  enter- 
ing water-gas,  cooled  by  interchange  with  hydrogen  is  next  par- 
tially liquefied  in  a  secondary  cooler,  composed  of  coils,  on  the 
outside  of  which  carbon  monoxide-rich  liquid  is  allowed  to  vapor- 
ise at  atmospheric  pressure.  The  latent  heat  of  vaporisation  of 
the  liquid  is  withdrawn  from  the  entering  gases  and  partial  lique- 
faction is  thus  attained.  Finally,  the  residual  gas  mixture  is  freed 
as  far  as  practicable  from  carbon  monoxide  and  nitrogen  still 
present  in  the  gas  by  passage  through  an  auxiliary  cooler  of 
liquid  air,  boiling  under  a  reduced  pressure  of  several  millimetres, 
the  lowest  practicable  temperature  being  thus  secured.  The  two 
fractions  are  separated;  the  hydrogen  fraction  passes  to  the  pri- 
mary heat  exchanger,  the  pressure  on  the  carbon  monoxide-nitro- 
gen liquid  is  released  and  the  liquid  mixture  is  driven  over  to  the 
secondary  cooler  for  vaporisation.  This  method  of  procedure 
is  illustrated  diagrammatically  in  the  accompanying  figure. 
(Fig.  IX.) 

A  variety  of  modifications  of  such  practice  have  been  sug- 
gested, more  especially  with  a  view  to  obviating  the  use  of  liquid 
air  as  additional  cooling  agent.  Where  the  hydrogen  is  required 
for  ammonia  synthesis  it  is  obvious  that  the  use  of  liquid  air 
simultaneously  offers  a  source  of  nitrogen,  since,  all  that  is  re- 
quired in  addition,  is  a  suitable  fractionation  column,  to  separate 
the  oxygen  and  nitrogen. 

By  allowing  the  hydrogen  leaving  the  chamber,  in  which  sep- 
aration of  carbon  monoxide  has  occurred,  to  expand,  with  per- 


94 


INDUSTRIAL  HYDROGEN 


formance  of  external  work,  an  additional  cooling  effect  may  be 
secured  with  further  separation  of  carbon  monoxide.  It  will  be 
seen  that  this  observation  of  Linde  is  a  special  feature  of  the 
Claude  (Soc.  L'Air  Liquide)  process  to  be  described  in  detail 
later.  Humboldt2  allows  the  hydrogen-rich  fraction  simply  to 
expand  to  normal  pressure,  additional  carbon  monoxide  is  de- 
posited and  the  hydrogen  passes  on  to  the  preliminary  heat  ex- 
changer to  cool  the  incoming  water  gas.  The  Badische  Co.  (D.  R. 
P.  285,703/13)  claim  the  use  of  a  water-gas  enriched  by  carbon 


Fid.  IX.     Diagrammatic  Representation  of  Linde-Frank-Caro  Liquefaction  Process. 

monoxide  and  nitrogen  from  the  vaporisation  process.  Since  both 
these  gases  show  a  large  positive  Joule  Thomson  effect,  extra 
cooling  is  realised  per  unit  of  hydrogen  produced.  In  this  way 
supplementary  liquid  air  cooling  is  to  be  avoided.  As  far  as  is 
known,  this  project  is  not  in  technical  use. 

The  Claude  Process. — According  to  the  claims  of  Claude  3 
the  compressed  and  purified  water-gas  is  pre-cooled  in  twin  heat 
interchangers,  one  half  of  the  water-gas  by  the  vaporised  carbon 

»F.   P.   445,883/1912. 

«  Soc.  L'Air  Liquide,  U.  S.  P.  1,135,355  and  1,212,455. 


HYDROGEN  FROM  WATER-GAS 


95 


monoxide,  the  other  half  by  the  expanded  hydrogen.  After  pass- 
ing through  these  preliminary  coolers  the  two  water-gas  streams 
unite  and  pass  to  the  separation  system  which  is  in  reality  a  com- 
plex tubular  reflux  condenser.  (See  Fig.  X.)  In  the  lower  half 
of  the  tubular  system  the  external  cooling  agent  is  the  vaporising 
carbon  monoxide-nitrogen  fraction.  In  the  upper  half,  hydrogen, 
which  has  been  expanded  with  performance  of  external  work,  is 


FIG.  X.     Diagrammatic  Representation  of  Claude  Liquefaction  Process. 

utilised.  The  separation  of  the  carbon  monoxide  occurs  within 
the  vertical  tubes.  The  progressive  lowering  in  temperature  with 
increasing  height  of  the  tube  may  be  noted.  The  lowest  end  of  the 
tubes  are  surrounded  by  carbon  monoxide-nitrogen  liquid  vapor- 
ising at  atmospheric  pressure.  Through  a  coil  immersed  in  this 
liquid  there  passes  also  the  compressed  carbon  monoxide  liquid 
from  the  collecting  vessel  in  the  base  of  the  separator.  The  com- 
pressed liquid  is  thereby  cooled.  In  an  auxiliary  heat  exchanger, 
expansion  of  the  liquid  to  atmospheric  pressure  occurs  and  the 


96  INDUSTRIAL  HYDROGEN 

liquid  flows  thence,  first  to  a  tank  in  the  uppermost  portion  of 
the  lower  half  of  the  separately  system,  and  then  to  the  lower 
half.  The  gases,  from  which  much  of  the  carbon  monoxide  has 
been  removed,  therefore,  come  in  contact  with  the  coldest  carbon 
monoxide  liquid.  The  liquid  is  coldest  because  it  contains  a 
certain  proportion  of  dissolved  hydrogen  which  lowers  the  boil- 
ing point.  In  the  upper  half  of  the  separator  the  process  is  a 
simple  heat  exchange  between  compressed  and  expanded  hydro- 
gen-rich gases.  If  the  auxiliary  heat  exchanger  and  the  tank  in 
the  upper  portion  of  the  carbon  monoxide  section  be  eliminated, 
simplification  ensues,  but  the  purity  of  hydrogen  obtained  is  not 
so  great. 

Composition  of  the  Two  Gas  Fractions.— As  shown  in  the  gas 
composition  flow  sheet  previously  given,  approximately  41  per 
cent  by  volume  of  the  original  water-gas  emerges  from  the  lique- 
faction process  in  the  hydrogen-rich  fraction.  The  carbon  mon- 
oxide fraction  comprises  a  further  41  per  cent  of  the  original 
water-gas,  losses  in  the  preliminary  purification  process  represent- 
ing some  15-20  per  cent  of  the  total  gas  input. 

The  normal  purity  of  hydrogen  obtained  corresponds  closely 
to  a  gas  of  the  following  composition: 

Hydrogen 97-97.5 

Carbon  monoxide 2-1.7 

Nitrogen 1-  0.85 

Of  the  total  impurity,  approximately  two  thirds  is  carbon 
monoxide  and  one  third  nitrogen.  In  steady  operation,  the  varia- 
tion is  slight,  but,  if  operation  be  intermittent,  the  percentage  of 
impurities  is  consistently  high.  For  the  first  few  hours  after 
starting  up  the  system  it  is  difficult  to  attain  a  purity  higher  than 
96  per  cent  hydrogen.  The  gas  prepared  by  this  process  is  re- 
markably free  from  water  vapor,  sulphur  and  phosphorus  com- 
pounds, though  this  freedom  is  attained  with  simultaneous  in- 
crease of  operational  difficulties.  For,  at  the  working  tempera- 
tures, these  impurities  are  solid  and  gradually  accumulate  in  the 
coils  of  the  liquefaction  system  causing  stoppages.  When  such 
choking  of  the  coils  has  occurred,  it  is  necessary  to  stop  the  proc- 
ess, warm  up  the  system  and  thaw  out  the  impurities.  As  a  con- 
sequence, an  extra  liquefaction  unit  is  to  be  recommended  to 
serve  as  a  standby  for  use  in  such  emergencies. 


HYDROGEN  FROM  WATER-GAS  97 

The  carbon  monoxide-rich  fraction  averages  75-80  per  cent 
carbon  monoxide  and  contains  in  addition  some  10-15  per  cent 
of  the  original  hydrogen  content  of  the  water-gas. 

Utilisation  of  the  Carbon  Monoxide  Fraction. — The  carbon 
monoxide-rich-gas,  after  evaporation,  is  utilised  as  a  source  of 
power  for  the  whole  plant.  Thus,  in  the  Badische  plant  at  Oppau, 
operating  with  the  Linde  process,  each  unit  of  35,000  cubic  feet 
capacity  was  equipped  with  a  gas  engine,  of  500  H.  P.,  which 
consumed  the  carbon  monoxide  produced  by  the  Linde  system. 
In  yet  another  plant,  of  smaller  capacity,  a  larger  engine  (Nur- 
emberg-Lilleshall)  of  800  H.  P.  was  installed  but  this  plant  was 
not  operating  to  full  capacity.  The  power  thus  furnished  is  ade- 
quate for  the  whole  of  the  plant  requirements.  From  a  single 
main  shaft  driven  by  the  gas  engine  there  may  be  simultaneously 
operated  (a)  the  water-gas  compressor,  (b)  the  air  compressor 
for  the  liquid  air,  (c)  the  water  compressor  for  the  carbon  di- 
oxide-removal plant,  (d)  the  ammonia  refrigeration  plant,  (e)  the 
blowers  for  the  water-gas  plant. 

Plant  Details. — The  water-gas  compressor  is  of  a  capacity 
equal  to  two  and  one-half  times  the  hydrogen  production.  A 
double-line  3-stage  compressor,  raising  the  pressure  to  300  Ibs. 
per  square  inch,  has  been  found  suitable  for  the  larger  units. 

For  air  compression  in  the  Linde  system  a  5-stage  air  com- 
pressor is  recommended.  The  capacity  of  this  compressor  varies 
largely  with  the  conditions  under  which  the  process  is  operated. 
The  actual  needs  of  auxiliary  liquid  air  or  nitrogen  are  small 
owing  to  the  high  efficiency  of  the  heat  exchanger  systems  and  the 
care  bestowed  on  the  lagging  of  the  plant.  Where,  however,  utili- 
sation may  be  made,  as  by-products,  of  the  nitrogen  and  oxygen, 
which  may  be  obtained,  it  follows  that  the  size  of  such  require- 
ments and  the  available  power  capacity  of  the  plant  will  de- 
termine the  size  of  the  liquid  air  auxiliary.  In  the  Oppau  plant 
sufficient  liquid  air  was  produced  to  supply  the  nitrogen  require- 
ments of  the  ammonia  synthesis  section  of  the  plant. 

Plant  and  operational  details  in .  the  case  of  the  pressure 
water-washing  process  of  carbon  dioxide  removal  will  not  receive 
extended  discussion  at  this  point  since  they  received  such  treat- 
ment in  the  account  of  the  operation  of  the  continuous  water- 
gas  catalytic  process.  (See  Chapter  III,  pp.  79-80.) 


98  INDUSTRIAL  HYDROGEN 

Since  carbon  dioxide  and  water  vapor  are  solid  at  the  temper- 
ature of  liquefaction  of  carbon  monoxide  the  removal  of  these 
impurities  must  be  most  rigorous.  Consequently,  the  gas  after 
treatment  with  water  under  pressure  is  freed  from  traces  of 
carbon  dioxide  by  a  supplementary  scrubbing  process  using 
caustic  soda  liquor.  This  may  best  be  accomplished  in  a  pres- 
sure scrubber  (see  p.  80)  or  by  passage  through  a  series  of 
pressure  wash  bottles.  Thus,  for  a  plant  treating  41,000  cubic 
feet  of  water-gas,  four  steel  wash  bottles  3  feet  in  diameter  by 
12  feet  high,  worked  in  sets  of  two,  each  set  for  12  hours  each, 
are  adequate  for  complete  removal  of  the  residual  carbon  dioxide 
from  the  water-washing  process. 

The  ammonia-refrigerator  plant  is  of  the  usual  type  as  far  as 
the  production  of  the  low  temperature  is  concerned.  The  system 
to  be  cooled  consists  of  a  set  of  coils  through  the  interior  of  which 
the  gas  to  be  freed  from  water  is  passed.  It  is  necessary,  how- 
ever, to  provide  duplicate  sets  of  the  coils  in  which  the  gas  under- 
goes the  cooling  process  since  they  become  choked  by  separation 
of  solid  impurities,  mainly  ice,  and  must  at  intervals  be  thawed 
out.  The  capacity  of  the  plant  is  readily  determined  by  the 
volume  of  water-gas  treated  and  by  the  maximum  moisture  con- 
tent of  the  gas  at  the  working  pressure. 

General  Remarks  on  the  Efficiency  of  the  Process.— The  pres- 
ent high  cost  of  fuel  centres  interest  at  once  on  the  ratio  of 
water-gas  consumed  to  hydrogen  output.  The  data  already  given 
show  that  this  ratio  is  2.5  to  1,  or  in  other  words  practically  the 
same  value  as  in  the  steam-iron  process  when  systematically 
controlled.  In  the  present  case,  the  extra  gas  is  used  to  produce 
power  for  plant  operation ;  in  the  steam-iron  process  it  is  used  for 
maintaining  the  reaction  temperature.  In  the  latter  process,  how- 
ever, an  additional  fuel  bill  for  steam  for  the  hydrogen  making 
reaction  is  generally  incurred,  though  it  is  undoubtedly  true  that 
this  could  be  more  than  supplied  in  a  well-ordered  plant  from 
the  waste-heat  of  the  process.  On  water-gas  consumption  the 
merits  of  the  two  processes  are  therefore  about  equal,  both,  how- 
ever, being  more  expensive  in  this  regard  than  the  water-gas  cata- 
lytic processes  previously  considered.  Plant  cost,  involving  fixed 
charges  on  a  large  amount  of  rapidly  moving  heavy  machinery, 
should  be  relatively  high.  Renewal,  however,  should  be  less  than 


HYDROGEN  FROM  WATER-GAS  99 

in  the  steam-iron  process  where  deterioration  of  the  retorts  and 
disintegration  of  the  contact  mass  represent  heavy  items  of  ex- 
penditure. A  much  higher  purity  is  readily  attained  in  the 
steam-iron  process  than  is  possible  in  the  simple  liquefaction 
process.  The  product  in  the  latter  case,  with  a  2  per  cent  carbon 
monoxide  content,  is  frequently  impossible  of  use  without  special 
purification.  Consideration  of  the  methods  of  such  purification 
will  be  specially  dealt  with  at  a  later  stage.  They  all  involve, 
however,  additional  expense.  Where  such  purification  is  not 
requisite  it  is  often  desirable  owing  to  the  higher  efficiency  of 
utilisation  that  is  possible.  Thus,  hydrogen  from  the  steam-iron 
process  is  undoubtedly  a  more  efficient  agent  for  the  hydrogena- 
tion  of  oils  although  the  product  of  the  simple  liquefaction  proc- 
ess is  in  use  for  such  purposes  (Bedford-Erdmann  process).  In 
the  Linde  system,  the  nitrogen  obtained  represents  an  item  in 
favor  of  the  process  when  the  hydrogen  is  to  be  used  for  am- 
monia synthesis.  But,  the  best  commentary  on  its  efficiency  as 
contrasted  with  the  water-gas  catalytic  process  hydrogen  for 
purposes  of  ammonia  synthesis  is  that  the  Badische  Co.  at 
Oppau,  and  later  at  Merseburg,  built  all  units,  subsequent  to  the 
first  three,  to  operate  the  catalytic  process. 

Miscellaneous  Physical  Methods  of  Preparing  Hydrogen  from 
Water  Gas  and  Other  Technical  Gases. 

Liquefaction  is  not  the  only  physical  agency  which  has  been 
proposed  for  the  production  of  hydrogen  from  water-gas.  Proc- 
esses based  on  diffusion,  centrifugal  action,  preferential  solu- 
bility and  on  solution  coupled  with  refrigeration  have  received 
attention. 

As  early  as  1891  Pullmann  and  Elworthy  suggested  the  pro- 
duction of  a  hydrogen-carbon  dioxide  mixture  by  interaction  of 
steam  and  incandescent  coke  and  the  separation  of  the  carbon 
dioxide  by  diffusion  through  diaphragms  of  plaster  of  Paris  or 
of  porous  porcelain.  The  same  proposals  relative  to  the  con- 
stituents of  water-gas  are  contained  in  a  French  patent  (372,- 
045/1906)  to  Jouve  and  Gautier,  unglazed  porcelain  to  be  used 
as  the  diffusion  medium.  The  proposal  is  revived  with  modifica- 
tions in  a  recent  patent  to  Snelling  (U.  S.  P.  1,174,631/1916)  ac- 
cording to  which  water-gas  is  to  be  resolved  into  its  constituents 


100  INDUSTRIAL  HYDROGEN 

by  diffusion  at  temperatures  above  800°  C.  through  porous  ma- 
terials, e.  g.,  alundum,  coated  with  platinum  or  palladium.  With 
such  a  coating  a  pressure-tight  septum  could  be  produced.  In 
such  case,  the  diffusion  process  could  be  accelerated  by  subject- 
ing the  gas  undergoing  diffusion  to  pressure. 

A  considerable  reduction  in  the  content  of  foreign  gases  present 
in  hydrogen  can  be  produced  in  this  manner.  Reductions  in  the 
carbon  monoxide  concentration  from  30  per  cent  to  5  per  cent  by 
one  diffusion  operation  are  recorded  in  the  patent  literature. 
The  time  factor,  however,  is,  in  general,  noticeably  absent  from 
such  specifications  and  yet  is  of  fundamental  importance  in  the 
technical  application.  It  is  hard  to  visualise  the  diffusion  proc- 
ess successfully  applied  in  the  industry. 

Numerous  proposals  to  separate  hydrogen  and  carbon  monox- 
ide by  centrifugal  action  have  been  made.  The  patent  specifica- 
tions of  Mazza  4  and  of  Elworthy5  are  suggested  for  reference. 
They  have  no  technical  significance. 

Dewar's  experiments  with  liquid  air  showed  that  hydro- 
carbons could  be  removed  from  coal  gas  by  cooling  the  latter 
to  liquid  air  temperatures.  Bergius  suggested  this  method 
of  purification  for  hydrogen  produced  by  his  process  (see  Chap- 
ter VI,  p.  123) ,  using  charcoal  cooled  in  liquid  air  as  absorbent 
for  the  impurities.  Curme  6  suggests  the  removal  of  condensible 
hydrocarbons  such  as  acetylene  and  ethylene  in  this  way,  methane 
and  hydrogen  passing  on  if  the  carbon  be  maintained  at  ordinary 
temperatures.  Soddy  7  similarly  utilises  this  property  of  char- 
coal to  remove  ethylene  and  benzene  from  coal-gas  and  coke-oven 
gas.  Adam 8  utilises  the  same  agent  for  removal  of  carbon 
disulphide  and  naphthalene  from  coal-gas. 

Considerable  attention  has  been  given  recently  to  a  proposal 
of  G.  Claude  9  for  the  preparation  of  hydrogen  from  mixtures 
such  as  coke-oven  gas.  The  patents  claim  the  production  of 
hydrogen  by  solution  of  the  other  constituents  in  solvents  such 
as  alcohol,  acetone  or  benzene  employing  very  high  pressures 
(500  to  2,000  atmospheres) ,  or  in  ether  at  —  60°  C.  at  pressures 

*B.  P.  12,194/1902. 

•B.  P.  10,581/1906. 

"U.    S.  P.  1,181,  116/1916. 

TB.   P.    125,253/1919. 

8TJ.  S.  P.  127,431/1919. 

BB.  P.  130,092/1918;  130,358/1918. 


HYDROGEN  FROM  WATER-GAS  101 

of  50  to  300  atmospheres.  Hydrogen  is  the  least  soluble  con- 
stituent of  the  mixtures.  It  is  a  moot  point,  however,  as  to  how 
much  more  soluble  the  other  gases  are  under  the  given  conditions. 
Published  data  are  lacking  on  this  point.  It  must  be  observed, 
however,  that,  unless  there  is  a  marked  solubility  differential 
between  hydrogen  and  the  other  gases,  the  process  will  be  im- 
possible merely  on  the  ground  of  hydrogen  losses  alone.  It  must 
be  remembered  that  these  losses  will  be,  in  the  purified  gas,  de- 
termined by  the  solubility  of  hydrogen  at  the  working  pressure  in 
the  solvent  chosen. 


Chapter  V. 

Hydrogen  by  Electrolysis. 

The  production  of  hydrogen  from  water  by  the  electrolysis 
of  dilute  aqueous  solutions  of  acids  or  alkalis  is  the  simplest 
method  of  producing  this  gas  which  is  operated  technically.  In 
the  last  analysis  these  processes  reduce  to  the  decomposition  of 
water  into  its  elements  with  the  aid  of  the  electric  current,  where- 
by, from  2  gram-mols  of  water,  2  gram-mols  of  hydrogen  and  1 
gram-mol  of  oxygen  are  simultaneously  produced 

2H20  =  2H2  +  02 

Given  a  well-designed,  well-constructed  electrolytic  hydrogen 
plant,  a  continuous  supply  of  hydrogen,  in  a  high  state  of  purity, 
with  a  minimum  of  labor  and  plant  control,  can  be  obtained 
with  a  high  degree  of  efficiency.  Offsetting  the  ease  of  production 
by  the  electrolytic  method,  however,  are  high  initial  plant  costs 
and  high  cost  of  electrical  energy  utilised  per  unit  of  hydrogen 
produced.  As  it  is  these  factors  which  tend  to  eliminate  electro- 
lytic hydrogen  from  extended  industrial  use,  a  careful  analysis 
of  their  importance  in  the  problem  will  first  be  considered.  This 
completed,  a  resume  of  typical  industrial  units  and  their  especial 
features  will  be  given. 

The  relationship  between  quantity  of  electricity  flowing  and 
the  volume  of  hydrogen  produced  is  given  by  the  laws  of  electrol- 
ysis first  enunciated  by  Faraday.  These  laws  state: 

(1)  The  quantity  of  an  electrolyte  which  is  decomposed  is 
directly  proportional  to  the  quantity  of  current  which  is  flowing. 

(2)  The  mass  of  a  substance  liberated  by  a  given  quantity 
of  electricity  is  proportional  to  the  equivalent  weight  of  the  sub- 
stance. 

The  equivalent  weight  of  an  element  is  equal  to  the  atomic 
weight  divided  by  the  valency.  Since  many  substances  have 
varying  valencies,  it  may  be  well  to  define  the  equivalent  weight 
in  reference  to  the  number  of  ionic  charges  which  the  substance 

102 


HYDROGEN  BY  ELECTROLYSIS  103 

is  carrying  in  the  solution  in  which  the  electrolysis  is  taking 
place.  In  such  case  the  equivalent  weight  is  the  weight  in  grams 
of  one  gram  ion  divided  by  the  number  of  ionic  charges  which 
the  ion  carries.  The  quantity  of  electricity  required  to  liberate 
one  equivalent  weight  of  any  substance  is,  by  Faraday's  second 
law,  always  the  same  and  is  96,500  coulombs  (ampere-seconds). 
Hence,  it  may  be  concluded  that  96,500  coulombs  liberate 

—  =  1  gram  of  hydrogen  (since  the  ion  is  H+)  or  for  oxygen 

16 

— •  =  8  grams  of  oxygen  (since  the  ion  is  0~~).  Correspondingly, 

56 

for  iron  in  ferric  chloride,  the  equivalent  weight  is  —  —  18.66 

3 

56 

grams  (since  the  ion  is  Fe+++),  but  in  ferrous  sulphate,  —  =28 

grams  (since  the  ion  in  this  case  is  Fe++). 

For  technical  purposes  it  is  more  convenient  to  calculate  with 
ampere-hours  instead  of  coulombs  and  with  gas  volumes  in  place 
of  equivalent  weights.  The  following  list  gives  some  of  the  more 
important  constants  in  reference  to  the  relationships  existing  be- 
tween quantity  of  current  and  gas  volumes  produced  in  electro- 
lytic processes  yielding  hydrogen  and  oxygen: 

1  Ampere-hour  liberates  0.03731  gram  equivalents. 

1  Ampere-hour  liberates  0.01482  cub.  ft.  of  dry  hydrogen 
at  N.  T.  P. 

1  Ampere-hour  liberates  0.00741   cub.   ft.  of  dry  oxygen 
at  N.  T.  P. 

1  Ampere-hour  liberates  0.01585  cub.  ft.  of  dry  hydrogen 
at  20°  C.  and  760  mm.  pressure. 

1  Ampere-hour  liberates  0.00792  cub.  ft.  of  dry  oxygen  at 

20°  C.  and  760  mm.  pressure. 

1,000  cub.  ft.  of  hydrogen  at  20°  C.  and  760  mm.  pressure  re- 
quire approximately  63,000  ampere-hours  for  their 
generation  by  electrolysis. 

Consideration  may  now  be  given  to  the  other  factor  operating 
in  the  problem  of  necessary  electrical  energy  for  the  process,  the 
intensity  factor  or  decomposition  potential  required. 


104  INDUSTRIAL  HYDROGEN 

Theoretically,  the  work  necessary  to  produce  the  two  gases 
hydrogen  and  oxygen  from  water  by  the  aid  of  the  electric  cur- 
rent is  exactly  equal  to  the  work  which  may  be  produced  when 
these  two  gases  operate  as  gas  electrodes  in  a  reversible  cell,  the 
reaction  occurring  being  the  production  of  water.  Independent 
methods  of  deduction  of  this  work  quantity  based  upon  thermo- 
dynamical  reasoning  and  on  experimental  observation  show  that 
the  electromotive  force  of  a  hydrogen-oxygen  cell  should  be  in 
the  neighbourhood  of  1.23  volts.1  Hence,  an  electromotive  force 
of  1.23  volts  should  be  capable  of  liberating  hydrogen  and  oxy- 
gen continuously  from  an  aqueous  solution  of  an  acid  or  an 
alkali  having  electrodes  of  platinum  were  other  effects  not  present. 
It  has  been  shown,  however,  by  many  investigators,  that  the  min- 
imum voltage  necessary  for  the  continuous  decomposition  of 
water  in  a  solution,  for  example,  of  sodium  hydroxide,  with  plat- 
inum electrodes,  is  in  the  neighbourhood  of  1.7  volts.  Further- 
more, the  decomposition  voltage  is  dependent  on  the  nature  of 
the  electrode  material,  on  the  current  density  and  on  various 
other  variables  in  the  process.  Even  during  the  process  of 
electrolysis,  the  requisite  Voltage  may  change  with  changes 
brought  about  in  the  solution  by  the  electrolytic  process. 

The  cause  of  the  divergence  between  the  electromotive  force 
obtainable  from  a  reversible  hydrogen  and  oxygen  cell  having 
platinum  as  the  medium  for  the  gas  electrodes,  and,  on  the  other 
hand,  the  decomposition  potential  required  for  continuous  electrol- 
ysis of  aqueous  alkali  or  acid  solutions  with  platinum  electrodes, 
is  to  be  sought  in  the  phenomenon  of  over- voltage.  Experimenta- 
tion shows  that  the  behaviour  of  the  platinum  electrode  at  which 
hydrogen  is  being  liberated  is  practically  normal.  At  the  electrode 
liberating  oxygen,  however,  an  electromotive  force,  greater  than 
that  which  oxygen  is  capable  of  yielding  when  acting  as  gas 
electrode,  is  required  to  bring  about  the  continuous  liberation  of 
oxygen  gas  from  the  solution.  This  excess  electromotive  force 
represents  in  this  particular  case  the  over-potential  or  over- 
voltage. 

With  other  electrodes  than  platinum,  the  phenomenon  of 
over-voltage  is  not  confined  to  the  oxygen  electrode.  The  re- 
versible discharge  of  hydrogen  on  a  platinum  electrode  becomes 
irreversible  on  other  metallic  electrodes.  Thus,  polished  nickel 

1  Lewis,  Z.  phvsik.  Chern.,  1906,  55,  449. 


HYDROGEN  BY  ELECTROLYSIS 


105 


has  a  hydrogen  over- voltage  in  excess  of  that  of  polished  platinum 
by  about  0.12  volt,  iron  an  over-voltage  of  0.08  volts.  Since 
these  metals  from  the  principal  constituents  of  the  electrode  ma- 
terials for  hydrogen-oxygen  electrolytic  generators  it  is  of  in- 
terest to  tabulate  the  respective  over-voltages  in  respect  to  each 
gas  and  to  compare  the  data  with  the  corresponding  figures  for 
platinum. 


Electrode 
Material 

Oxygen 
Over-voltage  2 

Hydrogen 
Over-voltage  3 

Total 
Over-voltage 

Polished    plati- 
num   

0.44 

0.09 

0.53 

Platinised  plati- 
num   

0.24 

0.005 

0.245 

Polished  nickel. 
Spongy  nickel.  . 
Iron   

0.12 
0.05 
0.24 

0.21 
0-08 

0.33 
0.32 

Cobalt     .  .  .... 

0.13 

It  is  thus  evident  that  nickel  electrodes  require  the  least  ex- 
cess voltage  to  overcome  irreversibility  of  the  electrodes  with 
reference  to  the  two  gases.  As  iron  is  not  greatly  inferior  to 
nickel,  however,  in  this  respect,  and  as  it  is  a  considerably  cheaper 
electrode  material,  it  follows  that  iron  will  as  a  rule  be  the  pre- 
ferred metal  for  electrodes.  These  theoretical  considerations  sug- 
gest however  that  nickel-plated  iron  would  be  a  suitable  electrode 
material  and  it  will  be  shown  later  that  this  material  has  come 
into  extended  use.  A  nickel-plated  anode  and  an  iron  cathode 
would  represent  the  best  electrode  arrangements  of  these  two 
metals  from  the  standpoint  of  over-voltage. 

The  secondary  factors  influencing  over-voltage  are  current 
density,  composition  of  electrolyte  and  nature  of  the  electrode 
surface.  The  first  two  factors  are,  however,  of  so  much  greater 
importance  in  respect  to  the  other  properties  of  the  cell,  such  as 
electrode  area  and  strength  of  solution  employed,  which  governs 
internal  resistance,  that  their  effect  on  the  excess  voltage  required 
is  of  secondary  importance.  The  influence  upon  over-potential 

2  Coehn  and  Osaka,  Z.  anorg.  Chem.,  1903,  H,  86. 
8  Caspari,  Z.  physik.  Chem.f  1899,  SO,  89. 


106  INDUSTRIAL  HYDROGEN 

exercised  by  the  nature  of  the  electrode  surface  is  worthy  of 
consideration  in  respect  to  economy  of  electrical  energy.  Rideal 
has  shown  4  in  the  case  of  copper  and  zinc  that  the  change  from 
a  bright  microcrystalline  surface  to  an  amorphous  surface  is  ac- 
companied by  a  continuous  decrease  in  the  over-potential  of  an 
electrode.  If  the  same  holds  true  for  nickel,  it  would  be  antici- 
pated that  from  the  standpoint  of  over-voltage  the  ideal  electrode 
material  would  be  iron  with  a  firmly  adhering  coating  of  amor- 
phous nickel. 

Assuming  a  true  decomposition  potential,  in  absence  of  over- 
potential,  equal  to  1.23  volts,  it  follows  that  the  minimum  de- 
composition potential  with  over-voltage  from  technically  feasible 
electrodes,  and  that,  therefore,  of  practical  importance,  is  in  ex- 
cess of  1.5  volts.  The  actual  value  will  vary  with  the  electrolyte 
chosen  and  with  the  operating  conditions. 

In  practice,  such  voltages  are  however  impracticably  low,  due 
to  the  resistance  of  the  electrolyte  and  to  the  presence  in  the  cell 
of  devices,  generally  diaphragms,  inserted  to  prevent  intermixing 
of  the  gases.  In  attaining  this  latter  end,  the  resistance  of  the 
cell  is  increased  and  as  a  consequence  the  applied  voltage  must 
be  raised.  Voltages,  therefore,  of  2  to  4  volts  per  cell  are  usual 
in  electrolytic  hydrogen  production. 

The  resistance  of  the  electrolyte  to  the  passage  of  the  current 
is  reduced  to  the  lowest  possible  limit  by  employing  solutions  of 
electrolytes  showing  maximum  conductivities.  Thus,  alkaline 
electrolytes  containing  10-30  per  cent  alkali  are  in  use.  Certain 
early  commercial  units  employed  sulphuric  acid  solutions;  for 
example,  the  Schoop  cell  (1900)  used  acid  having  a  density  of 
1.235  (32.0  per  cent  H2S04).  Difficulties  due  to  corrosion  in  the 
cells  have  practically  led  to  the  abolition  of  the  acid  cells  and 
most  modern  units  are  made  with  alkaline  electrolytes.  The 
heat  produced  by  the  resistance  of  the  electrolyte  is  conserved, 
a  working  temperature  of  70°  C.  being  maintained  within  the  cell. 
This  increased  temperature  tends  also  to  diminution  of  resistance 
and,  hence,  to  decrease  of  applied  voltage  and  higher  energy 
efficiency. 

Mechanism  of  Electrolysis. — The  electrolytic  dissociation  of 
pure  water  into  hydrogen  and  hydroxyl  ions 

*J.  Am.  Chem.  Soc.  1920,  42,  104.  In  this  article  may  also  be  found  a 
discussion  of  over-voltage  together  with  a  literature  r€sum6  of  the  subject. 


HYDROGEN  BY  ELECTROLYSIS  107 

HOH  =  H+  +  OH- 

is,  as  is  well  known,  extremely  small  in  magnitude.  Addition  of 
hydrogen  ions  in  the  form  of  sulphuric  acid  will  diminish  the 
concentration  of  hydroxyl  ions  in  agreement  with  the  law  of  mass 
action  applied  to  electrolytic  dissociation.  Similarly,  addition  to 
water  of  hydroxyl  ions  in  the  form  of  alkaline  hydroxides  will 
suppress  the  hydrogen  ion  concentration  of  water.  Consequently 
the  conclusion  is  inevitable  that  in  such  solutions  the  formation 
of  hydrogen  and  oxygen  by  electrolysis  is  not  due  to  the  simul- 
taneous discharge  of  the  two  ions  as  indicated  in  the  equations 

20H-  +  2+  =  0  +  H20. 
H++    -  =  H. 

Secondary  reactions  predominate  in  either  acid  or  alkaline  elec- 
trolytes. Thus,  with  potassium  hydroxide  solutions,  the  hydrogen 
forming  reaction  is,  in  the  main,  undoubtedly,,  the  interaction  of 
discharged  potassium  ions  with  water. 

K+  +  -  +  H20  =  K  +  H20  =  KOH  +  H. 

In  solutions  of  sulphuric  acid,  the  oxygen  is,  correspondingly, 
chiefly  produced  by  reaction  with  water  of  discharged  sulphate 
ions 

S04  -  +  2  -  +  H20  ±±  S04  +  H20  =  H2S04  +  0. 

When  a  solution  of  a  neutral  salt  is  electrolysed,  both  hydrogen 
and  oxygen  are  the  products  of  secondary  reactions,  as  is  readily 
indicated,  for  example,  in  the  electrolysis  of  sodium  sulphate  so- 
lutions by  the  increasing  acidity  at  the  anode  and  the  increasing 
alkalinity  at  the  cathode. 

It  is  thus  evident  that  to  speak  of  the  industrial  production  of 
hydrogen  and  oxygen  by  electrolysis  as  the  electrolysis  of  water 
is  not  strictly  precise.  As  however,  apart  from  local  variations  in 
concentration,  the  net  change  in  the  solution  is  the  removal  of 
water,  the  term  is  frequently  applied  to  the  processes  under 
consideration. 

Earlier  Forms  of  Apparatus. — Examples  of  the  earlier  types 
of  apparatus  used  in  electrolytic  hydrogen  and  oxygen  production 
have  been  given  by  J.  W.  RichardsvL)  According  to  this  author 

*J.  Franklin  Inst.,  1905,   160,  387. 


108  INDUSTRIAL  HYDROGEN 

the  plant  installed  by  D'Arsonval  in  1885  probably  represents 
the  first  electrolytic  oxygen  generator  for  laboratory  purposes. 
A  thirty  per  cent  solution  of  sodium  hydroxide  served  as  electro- 
lyte, the  electrodes  were  of  cylindrical  sheet  iron  and  a  current 
density  of  2  amperes  per  square  decimeter  with  a  current  con- 
sumption of  60  amperes  was  employed.  Only  oxygen  was  col- 
lected and  the  anode  compartment  was  enclosed  in  a  woolen  bag 
which  served  as  diaphragm. 

Latchinoff 6  in  all  probability  constructed  the  first  large  scale 
apparatus.  He  employed  asbestos  cloth  diaphragms.  Using  an 
alkaline  electrolyte  of  10  per  cent  sodium  hydroxide  solution,  he 
employed  iron  electrodes,  a  current  density  of  3.5  amperes  per 
square  decimeter  and  an  applied  voltage  of  2.5  volts  per  cell. 
With  a  5-15  per  cent  sulphuric  acid  solution,  lead  anodes  and 
carbon  cathodes  were  employed.  Latchinoff  also  constructed  ap- 
paratus with  bipolar  electrodes,  the  one  side  of  the  electrode 
acting  as  cathode,  the  other  as  anode.  A  series  of  forty  cells  was 
used  on  an  ordinary  direct  current  lighting  circuit,  with  a  current 
density  of  10  amperes  per  square  decimeter.  In  yet  another  ap- 
paratus, electrolysis  was  conducted  under  pressure.  Compression 
to  120  atmospheres  was  possible,  the  containing  vessel  being  of 
heavy  iron.  A  system  of  floating  valves  kept  the  pressures  of 
the  two  gases  equal  in  the  apparatus. 

The  Garuti  process  originated  in  1892,  and  the  innovation 
then  made  was  the  use  of  metal  diaphragms  to  decrease  the  in- 
ternal resistance  and  to  avoid  expense  in  upkeep  of  porous  dia- 
phragms. It  was  found  that  the  metal  diaphragm  does  not 
function  as  a  bipolar  electrode  provided  it  does  not  reach  to  the 
bottom  of  the  cell  and  provided  the  applied  voltage  is  kept  be- 
low twice  the  decomposition  voltage  of  the  electrolyte  or  in  other 
words  below  about  3.0  volts.  The  original  cells  were  made  of 
sheet  lead  and  were  filled  with  dilute  sulphuric  acid  as  electrolyte. 
Subsequent  designs  employed  sheet  iron  for  electrodes  and  dia- 
phragms, and  sodium  hydroxide  solutions.  The  electrodes  were 
spaced  about  12  mm.  apart,  the  diaphragm  in  between  being  per- 
forated with  small  holes  in  the  lower  parts.  (Garuti  and  Pom- 
pili  B.  P.  23,663/1896.)  This  feature  still  further  reduced  the 
internal  resistance  of  the  cell.  In  modern  units  of  the  Garuti  cell 
all  soldering  of  joints  is  avoided.  The  metal  diaphragm  projects 

«B.  P.  15,925/1888. 


HYDROGEN  BY  ELECTROLYSIS  109 

below  and  is  insulated  from  the  electrodes  by  a  wooden  comb 
the  teeth  of  which  serve  to  space  the  electrodes.  The  diaphragm 
is  perforated  opposite  to  the  centres  of  the  electrodes  and  the 
holes  are  covered  with  wire  gauze  in  order  to  minimise  admixture 
of  the  gases.  A  series  of  the  cells  are  arranged  together  and 
immersed  in  a  single  tank  of  electrolyte.  The  gases  are  col- 
lected in  their  respective  mains,  hydraulic  seals  being  employed 
to  prevent  pressure  increase  and  mixing  of  the  gases.  The 
electrolyte  used  varies.  Sodium  hydroxide  in  10-30  per  cent 
solution  has  been  used  as  well  as  26  per  cent  potassium  hydroxide 
solution.  The  applied  voltage  is  about  2.5  volts  per  cell.  Cur- 
rent densities  of  25-30  amperes  per  square  foot  are  possible.  A 
current  efficiency  of  96  per  cent  is  claimed.  The  Garuti-Pompili 
cell  is  an  excellent  example,  therefore,  of  the  metal  diaphragm 
cell.  It  has  been  employed  in  this  country  by  the  American 
Oxhydric  Co. 

The  Schmidt  process 7  introduced  the  filter  press  type  of  cell, 
the  metallic  units  of  the  system  functioning  as  bipolar  electrodes 
on  one  face  of  which  hydrogen  is  evolved  and,  on  the  other,  oxy- 
gen. The  gases  are  kept  from  intermixing  by  means  of  asbestos 
or  other  non-conducting  porous  diaphragms,  the  gases  being  led 
away  from  the  generator-space  by  channels  similar  to  those  used 
in  filter-press  practice  for  the  discharge  of  the  filtrate.  The 
number  of  bipolar  units  in  series  with  one  another  is  determined 
by  the  current  available.  Thus  a  40  electrode  unit  is  suitable  for 
a  direct  current  supply  at  110  volts.  The  electrodes,  which  vary 
in  form  and  shape  as  do  filter  presses,  are  separated  from  one 
another  and  insulated  by  the  diaphragm  which  is  reinforced  at 
the  edges  and  on  both  sides  with  rubber  in  the  shape  of  the 
outside  flange  of  the  electrode.  Distilled  water  is  supplied  to  the 
system  from  a  tank  situated  at  a  higher  level  than  the  cells  by  a 
pipe  system  passing  to  channels  formed  by  holes  in  the  base  of 
the  electrodes.  To  these  channels  also  flows  the  spray  separated 
from  the  evolved  gases  in  the  gas-collecting  chambers  placed 
alongside  the  water  supply  tank. 

Various  strengths  of  alkali  hydroxide  and  alkali  carbonate 
solutions  have  been  employed  in  the  filter  press  type  of  cell.  The 
voltage  drop  varies  from  2.3  to  2.8  volts  *per  cell  while  amperages 
averaging  20  to  30  amperes  are  common. 

T  D.  R.  P.  111,131/1899. 


110  INDUSTRIAL  HYDROGEN 

The  filter  press  type  is  compact  and  simple  in  construction. 
It  requires,  however,  a  frequent  overhauling  to  maintain  it  in  a 
gas-tight  condition,  free  also  from  leaks  in  the  liquid  system. 

Plants  of  the  filter  press  type  are  made  in  this  country  by 
Schriver  and  Co.,  of  Harrison,  N.  J.,  and  the  International  Oxy- 
gen Co.,  of  Newark,  N.  J.  In  Europe,  erection  of  Schmidt  units 
has  been  undertaken  by  the  Oerlikon  Co. 

Schoop  8  devised  an  electrolyser  having  electrodes  surrounded 
by  non-porous,  non-conducting  diaphragms.  A  cylindrical  cell 
contains  two  anodes  and  two  cathodes,  the  electrodes  consisting 
of  tubular  metal  cylinders  completely  surrounded  by  clay  or 
glass  collecting  cylinders.  Both  anodes  and  cathodes  are  placed 
diametrically  opposite  to  one  another  in  the  cylinder,  the  evolved 
gas  being  led  off  to  the  mains  by  effluent  pipes  connected  to  the 
electrodes  of  like  polarity. 

Both  acid  and  alkaline  electrolytes  have  been  used  with  the 
Schoop  type  of  cell.  With  aqueous  sulphuric  acid  as  electrolyte, 
a  lead  tank  and  lead  electrodes  were  used.  The  voltage  required 
in  such  case  is  high  and  of  the  order  of  3.6  volts.  With  alkaline 
electrolytes  iron  is  the  metal  used  and  a  voltage  drop  of  2.25  volts 
is  adequate. 

The  Schuckert  system  employs  a  bell-collecting  system.  Iron 
electrodes  are  placed  in  a  tank,  alternately  anode  and  cathode. 
Over  each  electrode  is  placed  an  iron  bell,  the  bells  being  sep- 
arated from  each  other  by  a  screen  of  insulating  material  which 
projects  the  full  breadth  and  depth  of  the  containing  tank.  This 
tank  is  insulated  from  the  electrodes  and  does  not  play  any  part 
in  the  electrolysis.  A  tank  usually  contains  four  anodes,  four 
cathodes  and  eight  collecting-bells  from  four  of  which  hydrogen 
is  led  off  by  pipes  to  the  main,  oxygen  being  removed  from  the 
others.9  An  electrolyte  of  20  per  cent  sodium  hydroxide  solution 
is  normally  employed.  The  floor  space  required  is  comparatively 
large.  Several  plants  on  this  system  have  been  erected  in  this 
country. 

The  International  Oxygen  Co.,  in  an  early  form  of  the  unit 
systems  now  common  in  electrolytic  hydrogen  and  oxygen  pro- 
duction, used  a  tank  cell  in  which  the  tank  served  as  cathode. 
The  tank  was  of  steel  and  was  mounted  on  insulators;  it  had  an 

•Austrian  Patent  1,285/1900. 
•Cf.  Burdett  Cell,   p.  117. 


HYDROGEN  BY  ELECTROLYSIS  111 

annular  ring  to  hold  water  at  the  top  and  was  closed  by  means 
of  an  insulated  iron  cover.  To  this  cover  was  attached  an  anode 
in  the  form  of  a  cylinder  perforated  with  holes,  the  tank  being 
divided  into  two  compartments  by  an  asbestos  sack  suspended 
from  a  non-conducting  perforated  plate  around  the  anode  lead. 
The  top  of  the  compartments  was  sealed  by  means  of  two  hy- 
draulic seals,  formed  by  two  flanges  projecting  downwards  from 
the  cover  of  the  tank,  the  one  somewhat  larger  than  the  anode 
projecting  into  the  solution  of  electrolyte,  the  other  sealing  the 
exit  from  the  cathode  by  projecting  into  the  water-filled  annulus. 
Oxygen  from  the  anode  was  collected  within  the  inner  flange  and 
passed  away  through  an  exit  pipe  to  the  collecting  mains.  Hy- 
drogen generated  on  the  tank  walls  passed  on  the  outside  of  this 
flange  to  its  exit  pipe. 

The  cells  operated  at  an  average  voltage  of  2.6  volts  per  cell. 
They  had  a  current  capacity  of  400  amperes  per  unit  with  an 
output  of  about  6  cubic  feet  of  hydrogen  and  3  cubic  feet  of 
oxygen  per  cell  per  hour. 

Modern  Forms  of  Plant. — The  tendency  in  design  of  plant  for 
electrolytic  hydrogen  and  oxygen  in  recent  years  has  been  in  the 
direction  of  increased  economy  of  necessary  floor  space.  Fur- 
thermore, the  production  of  units  having  a  largely  increased  cur- 
rent capacity  is  now  engaging  the  most  serious  attention  of  the 
constructional  engineers  of  the  electrolytic  gas  industry.  The 
object  in  such  case  is  a  diminution  of  the  capital  cost  of  the  neces- 
sary plant,  to  bring  it  more  approximately  into  line  with  the 
outlay  involved  in  the  production  of  these  gases  by  other  methods. 
In  the  case  of  oxygen,  liquid  air  oxygen  has  been  the  active  com- 
petitor, while,  with  hydrogen,  any  other  of  several  well-tried 
chemical  processes  can  be  erected  at  a  very  much  lower  capital 
cost  for  an  equivalent  output.  The  purity  of  gas  product  which 
is  possible  by  processes  of  electrolysis  is  the  principal  reason  for 
energetic  prosecution  of  attempts  to  cheapen  and  improve  the 
electrolytic  processes. 

The  trend  in  design,  as  well  as  the  manner  in  which  safety 
and  surety  of  operation  are  being  secured,  may  conveniently  be 
demonstrated  by  describing  the  plants  which  modern  electrolytic 
gas  manufacturers  are  producing.  The  descriptions  given  in  the 


112  INDUSTRIAL  HYDROGEN 

following  are  largely  taken  from  the  excellent  bulletins  which 
these  manufacturers  issue. 

The  International  Oxygen  Company's  Type  4-1000  Unit  Gen- 
erator.— The  most  recent  form  of  electrolytic  hydrogen  and  oxy- 
gen generator  which  this  organisation  produces  is  a  unit-type  gen- 
erator designed  with  a  view  to  simpler  mechanical  and  electrical 
construction,  occupying  a  minimum  amount  of  floor-space  per 
unit  of  gas  evolution  and  showing  high  operating  economy  and 
flexibility  of  load. 

As  the  term  "unit"  implies,  each  generator  is  self-contained 
and  complete  in  itself,  capable  of  generating  both  gases  at  a 
rate  determined  by  the  applied  amperage.  An  installation  is 
made  up  of  a  number  of  such  units,  the  number  being  determined 
by  the  quantity  of  the  gases  required. 

Each  of  the  units  in  the  latest  type  of  cell  requires  a  floor 
space  of  4  inches  by  40  inches  and,  with  the  necessary  pipe  con- 
nections, needs  a  head-room  of  about  6  feet.  (See  Fig.  XI.) 

The  unit  is  a  thin  cast-iron  box  made  in  rectangular  form  to 
which  is  bolted  two  cast-iron  side  plates  serving  as  electrodes. 
The  cavity  between  the  electrodes  is  divided  by  a  diaphragm  of 
asbestos  fabric  clamped  directly  by  metal,  rubber  or  cement  of 
any  kind  being  conspicuously  absent.  This  diaphragm  forms  the 
two  chambers  of  the  cell. 

In  the  upper  part  of  the  rectangular  box  frame  are  reservoirs 
for  the  electrolyte,  from  which  it  is  fed  to  the  two  sides  of  the 
diaphragm.  The  two  gas  chambers  which  permit  the  separation 
of  the  gases  from  moisture  and  electrolyte  spray  are  also  located 
in  the  upper  part  of  the  cell  frame  and  serve  as  gas-traps  and 
gas  off-takes,  as  well  as  an  automatic  pressure-controlling  de- 
vice. At  the  bottom  of  the  frame  are  communicating  passage 
ways  which  permit  circulation  of  electrolyte  on  the  two  sides  of 
the  diaphragm.  In  the  base  of  the  cell  a  plug  valve  and  drain- 
ing device  is  provided  which  permits  the  electrolyte  to  be  drained 
from  the  cell  when  desired. 

The  cast-iron  electrodes  are  insulated  from  the  frame  and 
from  one  another.  A  heavy  packing  rim  of  insulating  material 
is  used,  and  the  bolts  which  hold  the  electrodes  to  the  frame  are 
insulated  by  mica  bushings.  The  electrodes  are  reinforced  by 
outside  ribs  and,  on  the  inside,  carry  a  great  number  of  pyramid- 


HYDROGEN  BY  ELECTROLYSIS 


113 


OXYGEN        wATte    HYDeOGCN 
OFFTAKE        rctD       OFFTAKC 


FIG.   XI.     International   Oxygen   Company's  Type  4-1000  Unit  Generator. 


114  INDUSTRIAL  HYDROGEN 

shaped  projections.  These  increase  the  electrode  area  in  con- 
tact with  electrolyte  and  facilitate  release  of  the  gases  at  the 
generating  surface.  The  inner  surface  of  the  cathode  is  specially 
treated  and  the  inner  surface  of  the  positive  electrode,  the  anode, 
is  heavily  nickeled.  In  this  way,  the  cell  uses  one  iron  and  one 
nickel  electrode  and  so,  the  over-voltage  is  minimised  (see  p.  105) 
and  electrical  efficiency  is  increased.  The  nickel  deposit  also 
prevents  the  formation  of  oxide  of  iron  which  occurs  with  iron 
electrodes  at  the  oxygen-yielding  electrode. 

The  diaphragm  is  impermeable  to  the  gas  bubbles  but  is  of 
a  texture  sufficiently  porous  to  avoid  development  of  too  high 
an  internal  resistance.  The  edges  of  the  diaphragm  are  held  be- 
tween a  flange,  projecting  inward  from  the  frame,  and  a  metal 
clamping  rim  bolted  to  this  flange. 

The  gas  off-takes  are  supported  on  insulated  brackets  which 
in  turn  rest  directly  on  the  cells.  They  are  fed  from  glass  bell- 
jars  which  form  part  of  the  insulation  between  the  cell  and  off- 
takes. The  bell-jars  also  act  as  indicating  devices  of  the  pres- 
sure in  the  off-take  lines.  The  cells  are  also  insulated  from  the 
earth  by  glass  insulators  protected  by  cast  iron  petticoats. 

The  normal  current  rating  of  the  cell  is  600  amperes  and  the 
voltage  required  at  this  amperage  is  2.2  volts.  The  gas  yield 
under  such  circumstances  is  4.8  cubic  feet  of  oxygen  and  9.6  cubic 
feet  of  hydrogen  per  clock  hour.  This  means  a  kilowatt  hour 
efficiency  of  3.65  cubic  feet  of  oxygen  and  7.3  cubic  feet  of  hy- 
drogen. 

The  cell  is  designed  to  operate  under  widely  varying  condi- 
tions of  current  with  a  high  level  of  efficiency.  Good  economy 
is  claimed  over  a  current  range  from  200  to  1,000  amperes.  At 
the  lower  figure  a  higher  electrical  efficiency  is  possible  since  the 
applied  voltage  per  cell  need  not  exceed  1.85  volts.  The  power 
consumption  per  unit  of  gas  produced  will  therefore  be  some  16 
per  cent  less  than  at  normal  rating,  or  a  production  of  8.7  cubic 
feet  of  hydrogen  per  kilowatt  hour.  The  yield  per  cell  per  unit  of 
time  will,  however,  be  correspondingly  smaller.  When  operating 
at  1,000  amperes  the  cell  requires  an  applied  voltage  of  about 
2.54  volts.  The  power  consumption  is  therefore  some  15  per  cent 
greater  than  at  normal  load.  This  corresponds  to  6.32  cubic  feet 
of  hydrogen  per  kilowatt  hour.  An  increased  yield  per  cell  per 
hour  is  attained.  This  wide  variability  in  current  range  repre- 


HYDROGEN  BY  ELECTROLYSIS          *       115 

senting  a  varying  hydrogen  yield  of  from  400  cubic  feet  to  2,000 
cubic  feet  of  hydrogen  per  24  hour  day  is  claimed  as  an  especial 
feature  of  the  Type  4 — 1,000  unit  generator.  Naturally  the  par- 
ticular mode  of  operation  chosen  will  depend  on  a  number  of  fac- 
tors, including  cost  of  current,  capital  cost  of  plant  and  nature 
of  the  gas  consumption,  whether  steady  or  variable. 

Compactness  of  plant  per  unit  of  gas  generated  is  also  claimed 
for  this  type  of  cell.  At  normal  rating  of  600  amperes,  the  pro- 
duction per  24  hours  is  somewhat  over  200  cubic  feet  of  hydrogen 
per  square  foot  of  floor  area.  At  1,000  amperes  this  figure  is 
raised  to  350  cubic  feet  of  hydrogen  per  24-hour  day. 

The  purity  of  the  gases  is  high,  the  hydrogen  being  purer  than 
the  oxygen.  Average  purities  claimed  are  99.7  per  cent  for  hy- 
drogen and  99.5  per  cent  for  oxygen-. 

The  Electrolabs  Levin  Generator. — This  generator  is  also  of 
the  unit  type  built  in  two  sizes,  Type  A  and  Type  B.  These  cells 
are  built  exactly  alike  except  as  regards  dimensions.  Type  A 
has  external  dimensions  of  30  inches  by  25  inches  by  G1^  inches 
and  a  rated  current  capacity  of  250  amperes.  Type  B  is  43  inches 
by  37  inches  by  8%  inches  with  a  normal  current  capacity  of  600 
amperes.  Under  normal  current  ratings  the  hourly  hydrogen 
yield  is  4  cubic  feet  in  the  smaller  type  and  9.6  cubic  feet  in  the 
larger  unit. 

The  Levin  cell  contains  three  compartments.  (See  Fig.  XII.) 
Oxygen  is  generated  in  the  two  outer  compartments,  hydrogen  in 
the  centre  compartment.  Two  sheet  metal  frames  carrying  two 
asbestos  diaphragms  serve  as  the  separating  media  between  the 
compartments.  The  electrodes  are  quite  independent  of  the  cas- 
ing, they  are  separated  from  and  securely  fixed  within  the  casing 
by  blocks  of  asbestos.  The  electrodes  are  plated,  the  cathode 
with  cobalt  the  use  of  which  is  a  special  patented  feature  of  the 
cell,  the  anode  with  nickel.  Rideal®  records  a  hydrogen  over- 
voltage  for  cobalt  varying  between  0.0  and  0.03  volts,  com- 
pared with  0.01  to  0.21  volts  for  nickel.  For  the  oxygen  over- 
voltage  Coehn  and  Osaka  record  for  cobalt  the  value  0.13  volt© 
An  alkaline  electrolyte  is  employed  in  the  Levin  cell. 

Each  compartment  has  a  separate  water  feed  which  also  serves 

10  Loc.  cit.  p.  106. 

11 Z.  anorg.  Chem.  1903,  3-4,  86. 


116 


INDUSTRIAL  HYDROGEN 


FIG.   XII.     The  Electrolabs   Levin   Generator. 

as  a  blow-off  device  to  vent  the  gas  from  each  compartment  un- 
der abnormal  conditions.  A  sight-feed  indicator  is  placed  be- 
tween the  cell  and  off-take  pipe,  isolating  the  cell  from  other  units 
in  the  group  and  also  serving  as  a  pressure  regulator  inside  the 
compartments  of  the  cell. 

A  special  feature  of  the  generator  is  that  each  unit  is  de- 
livered entirely  welded  and  completely  and  rigidly  assembled. 
There  is  thus  no  possibility  of  trouble  due  to  leaks  at  joints  in 
the  system.  The  weight  per  cell  per  unit  of  gas  produced  has 
been  reduced  in  this  cell  to  a  minimum  and  the  standardisation 
and  simplicity  of  parts  makes  for  rapidity  of  construction  and 
assembly. 

At  normal  ratings  an  applied  voltage  somewhat  over  2  volts 
is  apparently  sufficient.  The  purity  of  the  gases  produced  in  this 
generator  is  noteworthy,  records  cited  by  the  makers  for  opera- 


HYDROGEN  BY  ELECTROLYSIS  117 

tion  over  three  months  having  shown  an  average  of  99.85  per 
cent  for  oxygen  and  a  hydrogen  purity  still  higher.  This  points 
also  to  adequate  design  in  the  cell  to  ensure  safety  of  operation. 

Burdett  Manufacturing  Company's  Cells. — The  latest  B  and 
C-types  of  cell  produced  by  this  company  are  closed  multiple- 
electrode  cells  standing  in  an  open  rectangular  steel  tank  con- 
taining the  electrolyte  and  completely  submerged  in  the  liquid. 
In  this  way  the  gas  is  generated  underneath  the  liquid  and  any 
leakages  are  visible. 

The  C-type  of  cell  is  contained  in  a  steel  tank  17^4  inches  by 
31  inches  by  44  inches  high.  It  weighs  750  pounds  empty  and 
1,650  pounds  filled  with  its  solution  of  electrolyte.  The  multiple 
electrodes,  with  an  asbestos  diaphragm  between  each  electrode, 
divide  the  cell  into  seven  gas  compartments,  three  for  oxygen 
and  four  for  hydrogen.  The  asbestos  diaphragms  have  a  free  end 
at  the  base  of  the  cell,  thus  allowing  for  shrinkage,  a  feature  of 
superiority  claimed  for  this  diaphragm  over  the  rigidly  fixed 
type.  The  open  end  at  the  base  insures  uniform  density  of  elec- 
trolyte and  corresponding  uniformity  in  current  distribution 
owing  to  the  circulation  of  liquor  which  is  set  up  by  means  of 
the  several  gas  compartments  provided. 

The  gases  collect  in  the  upper  portions  of  the  cell  and  pass 
through  glass  lanterns  to  the  off-take  pipes.  The  lanterns  pro- 
vide for  observation,  washing  and  pressure  regulation  of  the  gas. 
They  also  serve  as  the  vehicle  through  which  fresh  distilled  water 
is  daily  fed  to  the  cells.  This  feeding  through  the  lanterns  pro- 
vides a  means  of  cleansing  these  latter  daily.  The  water  added 
is  led  from  the  lanterns  to  the  base  of  the  cell,  thus  ensuring  in- 
termixture with  the  electrolyte. 

With  an  electrolyte  of  sodium  hydroxide  solution,  between 
22-24°  Be.  in  strength,  the  normal  rating  of  the  cell  is  400  am- 
peres. Under  such  conditions  a  voltage  of  1.95  volts  per  cell  is 
adequate.  A  high  kilowatt-hour  efficiency  is  therefore  obtain- 
able, corresponding  to  4.08  cubic  feet  of  oxygen  or  8.16  cubic 
feet  of  hydrogen  per  kilowatt-hour.  The  efficiency  is  somewhat 
higher  at  lower  amperages  and  lower  with  increased  load.  At 
700  amperes  the  efficiency  is  6.9  cu.  ft.  of  hydrogen  per  K.  W.  H. 
and  at  300  amperes  the  efficiency  is  8.4  cu.  ft.  of  hydrogen  per 
K.  W.  H. 


118  INDUSTRIAL  HYDROGEN 

Consideration  has  been  given  by  the  Burdett  Co.  to  the  con- 
struction of  cells  having  much  higher  amperages  than  those  con- 
sidered above.  The  object  of  such  a  study  is  obviously  the  reduc- 
tion of  capital  cost  in  a  large  unit  upon  which  considerable  call 
for  gas  is  to  be  made.  If,  for  example,  a  2,500  ampere  cell  could 
be  constructed  at  a  capital  cost  only  some  2  to  3  times  as  great 
as  the  cost  of  a  400  ampere  cell,  then  the  installation  cost  of  a 
large  unit  would  be  approximately  halved.  These  considerations 
open  up  interesting  possibilities.  An  analysis  of  costs  for  capital 
charges  even  suggests  that  it  would  be  very  advantageous,  with 
a  source  of  cheap  power,  to  operate  the  present  C  type  cell  at 
considerably  higher  amperages  than  at  present  recommended,  in 
spite  of  the  lower  power  efficiency  thereby  resulting.  Operating 
at  4,700  amperes  with  a  modified  electrode  having  an  area  of 
4,500  square  inches,  with  caustic  soda  of  23°  Be.  as  electrolyte, 
such  a  cell  required  2.63  volts  with  a  working  temperature  of 
135°  F.  and  should  require  only  2.3  volts  at  the  normal  working 
temperature  of  160°  F.  The  interdependence  of  power  charge, 
output,  and  capital  cost  and  their  variability  from  place  to  place 
make  a  complete  discussion  of  the  problem  difficult.  Discussion 
of  the  problem  in  relation  to  alkali  chlorine  cells  has  received  a 
certain  degree  of  attention  recently^ 

The  engineering  difficulties  in  the  problem  of  high  amperage 
cells  are  adjudged  to  be  solved  by  the  Electrolabs  Co.  as  a  re- 
sult of  experiments  in  the  building  of  a  10,000  ampere-unit.  It 
has  been  found  that  a  unit  of  such  size  may  be  operated  at  a 
potential  drop  of  2.5  volts.  On  increasing  the  load  successively 
by  1,000  amperes  to  15,000  amperes,  it  was  found  that  an  addi- 
tional 0.1  volt  was  required  for  each  extra  1,000  amperes,  so  that 
when  operating  at  15,000  amperes  a  potential  of  3  volts  per  unit 
was  required.  It  has  been  estimated  that  a  plant  constructed 
from  such  units,  yielding  a  daily  output  of  2,000,000  cubic  feet 
of  hydrogen,  with  cheap  water-power  current,  could  deliver  hy- 
drogen at  a  cost  as  low  as  that  obtaining  in  the  case  of  gas  pro- 
duced by  the  cheapest  chemical  methods.  Even  in  such  circum- 
stances, however,  the  main  cost  is  apparently  equally  distributed 
between  capital  and  fixed  charges  on  the  one  hand  and  power 
on  the  other,  with  minor  fractions  only  going  to  labor  and  up- 
keep. 

"  See  Wheeler,  Chem.  d  Met.  Eny.f  1919,  tl,  437. 


HYDROGEN  BY  ELECTROLYSIS  119 

Operational  Procedure. — In  the  majority  of  cases  the  cells 
are  installed  by  the  makers  and  production  is  commenced  under 
the  supervision  of  their  staff.  For  satisfactory  operation,  subse- 
quently, a  definite  routine  procedure  is  necessary.  Attention 
should  particularly  be  directed  to  the  maintenance  of  water  level 
in  the  cells,  to  the  purity  of  the  gases  and  to  the  energy  con- 
sumption. Occasionally  a  systematic  check  of  the  electrolyte  and 
its  temperature  should  be  undertaken. 

Purity  tests  on  the  gases  produced,  when  frequently  and  regu- 
larly undertaken,  are  most  useful  indexes  of  the  general  well- 
being  of  the  cells.  A  loss  in  purity  of  even  one-tenth  of  one  per 
cent — which  will  be  soonest  apparent  in  the  oxygen  supply — 
should  be  traced  to  its  source.  This  can  most  easily  be  done,  first 
by  checking  battery  to  battery  in  the  whole  plant  to  determine 
which  is  producing  gas  of  low  purity.  The  battery  isolated,  the 
individual  cells  should  then  be  checked  until  the  exact  cell  has 
been  located  and  cut  out  of  the  system.  Automatic  recording  de- 
vices (see  Chapter  IX)  should  prove  of  marked  use  in  this  re- 
spect. 

It  is  to  the  breakdown  of  the  diaphragm  that  low  purity  is 
frequently  due.  The  composition  of  the  asbestos  employed  is  a 
factor  to  which  the  user  should  pay  special  attention.  It  is 
much  easier  and  cheaper  to  make  asbestos  cloth  with  cotton  as  an 
aid  in  strengthening  the  cloth.  But,  to  ensure  cell  efficiency,  cot- 
ton must  be  rigorously  excluded.  The  natural  tendency  of  the 
asbestos  to  shrink  in  time  leads  to  defects  and  hence  to  low 
purities. 

The  water-level  must  be  maintained  against  the  losses  by  the 
electrolysis  and  also  against  that  carried  away  by  the  gases 
which  leave  saturated  with  water  vapor  at  the  temperature  of 
the  off-take  pipe.  In  certain  cells  this  is  automatically  taken 
care  of,  the  water  being  fed  to  the  cells  from  a  tank  under  a  defi- 
nite pressure.  In  certain  unit  type  cells,  the  water-feed  acts  also 
as  a  vent  in  case  of  abnormal  gas  generation.  In  such  case  con- 
trol of  water  level  is  doubly  important. 

Voltage  tests  on  each  cell  are  to  be  recommended.  In  such 
way,  breakdown  of  insulation  may  be  detected  and  cells  of  low 
efficiency  can  be  isolated.  External  insulation  should  also  be 
periodically  examined.  Special  observation  of  connections  is 


120  INDUSTRIAL  HYDROGEN 

advisable — otherwise,  hot  contacts  between  terminal  and  elec- 
trode may  develop. 

By-Product  Electrolytic  Hydrogen. — Hydrogen  is  produced  as 
a  by-product  in  the  electrolytic  alkali  industry.  The  electrolysis 
of  brine  to  yield  caustic  soda 

2Na+  +  2C1-  +  2H20  =  2NaOH  +  H2  +  C12 

results  in  the  simultaneous  production  of  both  chlorine  and  hy- 
drogen, as  much  as  10,000  cubic  feet  of  each  of  the  gases  being 
generated  per  ton  of  caustic  soda  produced  by  electrolysis.  With 
100  per  cent  current  efficiency  each  ampere  hour  would  produce 
1.322  grams  of  chlorine,  1.491  grams  of  sodium  hydroxide  and 
0.0373  grams  of  hydrogen.  Actually,  ampere-hour  efficiencies  ob- 
tained in  practice  vary  from  90  to  98  per  cent,  the  remainder  of 
the  current  being  spent  in  secondary  reactions  or  in  overcoming 
the  same.  It  is  apparent,  however,  that,  in  this  electrolytic  proc- 
ess, the  hydrogen  must  remain  a  by-product  owing  to  the  bulk 
of  the  other  products  obtained,  for  which  satisfactory  disposal 
must  be  secured.  At  present  the  only  openings  in  this  direction 
seem  to  be  in  the  soap  industry  and  in  the  wood  pulp  and  paper 
trade.  In  the  former  there  is  a  definitely  determinable  capacity 
of  the  plant  to  use  up  caustic  soda  in  the  manufacture  of  soap 
and  of  chlorine  in  the  manufacture  of  bleach.  In  the  latter 
industry,  caustic  soda  and  bleach  may  be  similarly  used,  the 
one  if  the  soda  process  for  chemical  pulp  is  employed,  the  other 
for  bleaching  the  product. 

From  the  standpoint  of  energy  efficiency  also,  it  is  evident  that 
brine  electrolysis  will  be  used  for  caustic  soda  and  chlorine  as  the 
main  products  and  that  hydrogen  will  remain  a  by-product.  It 
has  been  shown  that  the  working  voltage  of  the  electrolytic  hy- 
drogen-oxygen cells  is  in  the  neighbourhood  of  2  volts.  Now, 
the  decomposition  voltage  of  brine  is  approximately  2.3  volts  and 
technical  cells  are  usually  operated  above  3  volts  and  occasionally 
as  high  as  J  volts.  The  energy  efficiency  of  the  cell  will  therefore 
vary  between  30  and  75  per  cent.  An  example  taken  from  a 
recent  publication12  concerning  this  matter  will  illustrate  the 
effect  of  this  on  yield  of  hydrogen  per  unit  of  electrical  energy. 
An  alkali  chlorine  cell  operated  with  a  current  of  840  amperes  at 

"HoTine,  Chem.  &  Met.  Eng.,  1919,  21,  71,  in  which  article  the  question 
of  efficiency,  energy  requirements  and  costs  is  treated  graphically. 


HYDROGEN  BY  ELECTROLYSIS  121 

a  potential  of  4.15  volts.     The  hydrogen  produced  per  hour 

11.4  X  1,000 

amounted  to  11.4  cubic  feet,  or  at  the  rate  of =  3.25 

840  X  4.15 

cubic  feet  per  kilowatt  hour.  In  the  hydrogen-oxygen  cells  the 
corresponding  figures  are  approximately  7-8  cubic  feet  per  hour. 
The  extra  energy  cost  involved  in  the  chlorine  cell  must  be  com- 
pensated for  by  the  extra  worth  of  the  alkali  and  chlorine  pro- 
duced as  contrasted  with  the  potential  value  of  oxygen  in  the 
district  in  which  the  process  is  conducted.  The  choice  of  process 
would  thereby  become  a  purely  economic  problem. 

The  various  types  of  electrolytic  alkali-chlorine-hydrogen 
cells  may  be  divided  into  three  classes  which  are  differentiated 
from  one  another  by  the  means  taken  to  minimise  interaction  be- 
tween the  primary  anode  and  cathode  products.  The  three  classes 
are: 

(a)  Diaphragm  processes 

(b)  Mercury  cathode  processes 

(c)  Bell  processes. 

In  the  diaphragm  process  the  anode  and  cathode  are  separated 
by  a  porous  partition  generally  of  moulded  asbestos,  placed  most 
successfully  in  close  contact  with  the  cathode.  The  flow  of  liquor 
is  from  anode  compartment  to  cathode  compartment  in  order 
to  prevent  flow  of  hydroxyl  ions  to  the  anodic  space.  The  liquor 
may  be  drawn  off  either  at  the  top  or  bottom  of  the  cells,  depend- 
ing on  the  relative  concentrations  of  brine  and  caustic  soda  when 
a  mixture  of  these  constitutes  the  cathode  liquor.  The  manifold 
varieties  of  these  cells  does  not  permit  of  extended  description  in 
this  text.  The  following  comprise  some  of  the  principal  types  and 
the  place  of  their  employment: — Griesheim  cells,  the  oldest 
commercially  successful  cells,  in  Bitterfeld  and  Rheinfelden,  Ger- 
many; the  Hargreaves-Bird  at  Middlewich,  England;  the  Town- 
send  cell  at  Niagara  Falls;  LeSueur's  at  Rumford,  Maine;  the 
Outhenin-Chalandre  and  Basle  cells  in  France,  Switzerland,  Italy 
and  Spain;  the  Billiter-Siemens  at  Niagara  and  in  Europe;  the 
Billiter-Leyken  in  Austria;  the  Finlay  in  Belfast,  Ireland;  the 
Allen-Moore  at  Portland  and  Philadelphia;  the  Nelson  in  Wesjb 
Virginia  and  Edgewood,  Maryland ;  the  Wheeler  in  Wisconsin  and 
the  Jewell  in  Chicago. 

The  mercury  process  uses  anodes  of  carbon  and  cathode  of 


122  INDUSTRIAL  HYDROGEN 

mercury.  Sodium  amalgam  is  formed  at  the  cathode,  and  is  then 
transferred  to  an  adj  acent  compartment  where  it  reacts  with 
water  to  form  caustic  soda  and  hydrogen,  regenerating  the  mer- 
cury. The  Castner-Kellner  type,  an  early  successful  cell,  is  in 
operation  in  England.  During  the  war  it  was  furnishing  hydro- 
gen in  the  compressed  state  from  the  plant.  Other  mercury  cells 
are  the  Whiting,  the  Wildermann,  the  Rhodin  and  the  Solvay- 
Kellner. 

The  bell  process  uses  neither  mercury  nor  diaphragm,  grav- 
ity effecting  a  partial  separation  of  caustic  liquor  and  brine. 
The  anodes  are  suspended  in  bells,  having  a  chlorine  gas  out- 
let. The  brine  is  admitted  at  the  anode  at  a  rate  such  that  it 
flows  past  the  cathode  faster  than  the  cathode  products  can 
diffuse  upwards.  In  the  Aussig,  which  is  the  original  bell  cell, 
the  soda  is  drawn  from  the  bottom  of  the  tank  which  may  be 
made  to  contain  as  many  as  twenty-five  bells.13 

The  utilisation  of  the  present  available  hydrogen  from 
such  sources  is  greatly  to  be  desired.  Most  of  it  is  now  wasted. 
If  satisfactory  methods  are  adopted  for  the  exclusion  of  air 
and  chlorine,  the  gas  obtained  is  of  a  high  purity.  Of  these  im- 
purities air  is  probably  the  more  objectionable  as  chlorine  can 
be  readily  removed  from  the  gas  before  being  compressed  for 
use,  whereas  the  nitrogen  from  the  air  is  practically  impossible 
to  remove  on  a  technical  scale. 

18  Full  descriptions  of  the  various  cells  of  all  types  are  to  be  found  in  text- 
books of  Industrial  Chemistry,  e.  g.,  Rogers,  p.  262,  1920  Edition;  also  see 
the  recent  technical  literature,  e.  fir.,  CJiem.  Trade  J.,  1920,  66,  464,  491,  521; 
1920,  67,  3.  Chcm.  &  Met.  Eng.,  1919,  21,  17,  69,  133,  370,  403,  436.  Trans. 
Am.  Electrochem.  Soc.,  April  23,  1921.  No.  25. 


Chapter  VI. 
Hydrogen  From  Water. 

The  Bergius  Process. 

This  interesting  chemical  process  for  the  liberation  of  hydro- 
gen from  liquid  water  has  received  experimental  investigation 
upon  a  semi-technical  scale.  Its  translation  to  the  technical  unit 
has,  so  far  as  is  known,  not  yet  been  accomplished,  although  the 
process  offers  very  considerable  possibilities  as  a  method  of  cheap 
hydrogen  production. 

The  process  is  based  on  the  observation  that  iron  and  liquid 
water  readily  react  in  the  neighbourhood  of  300°  C.  and  that 
carbon  and  liquid  water  react  at  a  somewhat  higher  temperature. 
In  the  temperature  interval  stated,  it  is  apparent  that  pressures 
as  great  as  the  vapor  pressure  of  water  at  such  temperatures 
must  be  employed.  Otherwise,  complete  vaporisation  of  the  wa- 
ter would  ensue.  Furthermore,  as  the  critical  temperature  of 
water  is  365°  C.  any  process  of  the  type  named  must  be  con- 
ducted below  this  temperature.  The  vapor  pressures  of  water 
in  the  given  region  of  temperature  may  be  deduced  from  the 
following  data:—1 

Temperature  °  C.  200  250  300  350 

Vapor  pressure  (atm.)  15.3  39  89  167 

The  fundamental  features  of  the  proposal  are  disclosed  in 
the  patent  applications  and  in  a  series  of  articles  relative  to  the 
process.2 

With  coke  in  presence  of  twice  its  weight  of  water,  contain- 
ing, as  catalytic  accelerator,  0.5  per  cent  of  dissolved  thallium 
chloride,  ready  reaction  occurs  at  340°  C.  with  production  of  hy- 
drogen and  carbon  dioxide. 

C  +  2H20  =  C02  +  2H2. 

'Battelli,  Mem.  d.  Torino  (2),  4»,  63,  (1892)  ;  Ramsay  and  Young,  Phil. 
Trans.  A.  183,  107,  (1892). 

»D.  R.  P.  254,593/1911;  259,030/1911;  262,831/1912;  277,501/1913.  TJ. 
S.  P.  1,059,817  ;  1,059,818.  J.  Soo.  Ohem.  Ind.f  1913,  32,  463. 

123 


124 


INDUSTRIAL  HYDROGEN 


The  operating  pressure  is  about  150  atmospheres,  the  water  vapor 
being  removed  from  the  gases  by  a  reflux  cooler  attached  to  the 
exit  tube. 

With  iron  and  liquid  water,  reaction  starts  at  temperatures 
somewhat  above  100°  C.  and  is  more  rapid  than  with  carbon  at 
corresponding  temperatures.  In  this  case  also,  reaction  is  accel- 
erated by  addition  of  electrolytes  such,  for  example,  as  ferrous 
chloride.  Metallic  couples  are  in  general  more  reactive  than 
iron  itself,  the  iron-copper  couple  being  especially  noted  in  this 
regard.  Such  metallic  couples  are  readily  produced  by  adding  to 
the  water  an  electrolyte  such  as  sodium  chloride,  introducing 
along  with  the  iron  a  plate  of  copper.  The  accelerating  effect 
of  such  arrangements  is  exemplified  by  the  following  table  of 
comparative  data: 


Reaction  Material 

T°C. 

Hydrogen  Gen- 
erated per  Hour 

Iron  —  pure  water    

300 

230  cc. 

Iron  —  water  —  FeCl2  

300 

1390  cc 

Iron  —  water  —  FeCl2  —  Cu   .  .  . 
Iron  —  water  —  FeCl2  —  Cu   .  .  . 

300 
340 

1930  cc. 
3450  cc. 

It  will  be  noted  from  the  last  two  sets  of  data  that  the  tem- 
perature coefficient  of  the  reaction  is  low,  as  one  would  antici- 
pate from  the  heterogeneous  nature  of  the  reaction.  According 
to  Bergius,  the  reaction  with  finely  divided  iron  is  not  merely 
a  surface  action  but  penetrates  into  the  material,  a  quantitative 
conversion  of  the  iron  to  ferrous- ferric  oxide  resulting. 

3Fe  +  4H20  =  Fe304  +  4H2  +  38,400  calories. 

The  output  per  unit  of  reactant  volume  should  therefore  be  ma- 
terially enhanced. 

The  reaction  may  be  conducted  in  externally  heated  steel 
bombs;  when  it  has  once  started,  the  reaction  is  sufficiently  ex- 
othermic to  be  thermally  self-sustaining  as  indicated  by  the  ap- 
proximate value  given  in  the  preceding  equation,  and  further 
outside  heating  may  be  discontinued.  The  pressure  under  which 
the  reaction  is  carried  out  is  also  self-produced,  first  by  the 


HYDROGEN  FROM  WATER  125 

steam  and,  in  the  later  stages,  by  the  hydrogen,  which  is  only 
drawn  off  as  the  desired  operating  pressure  is  exceeded. 

In  the  experimental  unit  investigated  at  Hanover,  Germany, 
the  reaction  mixture  was  contained  in  an  iron  vessel  inserted  from 
the  bottom  in  a  steel  bomb  which  was  closed  by  a  high  pressure 
joint  of  the  LeRossignol  type  comprising  a  line  joint  between  a 
conical  plunger  and  socket  of  slightly  larger  angle.  The  con- 
taining vessel  served  as  a  protection  to  the  interior  of  the  bomb 
against  attack  by  steam.  The  vessels  were  fitted  with  a  reflux 
condenser  to  return  evaporated  water  to  the  system.  The  hy- 
drogen was  delivered  directly  to  cylinders  at  a  pressure  of  150 
atmospheres.  A  cubic  foot  of  useful  reaction  space  generated 
about  150  cubic  feet  of  hydrogen  per  hour.  Elsewhere,  it  is  stated 
that  a  90  per  cent  conversion  is  attained  in  4  hours.  Hence,  a 
yield  of  600  cubic  feet  per  cubic  foot  of  charge  represents  a 
conservative  estimate  of  the  hydrogen  generated. 

Discussing  the  large-scale  possibilities  of  the  process  Bergius 
points  out  that  it  was  possible  to  obtain  in  Germany  in  1913  steel 
bombs  of  the  necessary  specification  as  to  strength  having  a  re- 
action space  of  35  cubic  feet  each.  With  such  a  unit,  a  batch 
yield  of  20,000  cubic  feet  should  be  possible  and  a  daily  output 
of  100,000  cubic  feet.  The  regeneration  of  the  ferrous-ferric 
oxide  which  is  formed  by  the  reaction  can  be  effected  by  heating 
with  carbon  to  1,000°  C.  and  this  reduction  process  should  be 
possible  with  not  more  than  2  per  cent  of  carbon  remaining  in 
the  mass  on  completion  of  the  process. 

Gas  Purity. — A  high-grade  hydrogen  is  produced,  it  is  claimed, 
by  this  process.  Analysis  of  a  200  litre  sample  gave  the  follow- 
ing gas  composition: 

Hydrogen 99.95  % 

Carbon  monoxide +-.       0.001 

Saturated  hydrocarbons  0.042 

Unsaturated  hydrocarbons 0.008 

Too  much  emphasis  should  not  be  placed  upon  such  an  analysis, 
since  the  carbon  content  of  the  iron  employed  is  not  stated.  It  is 
asserted,  however,  that  the  carbon  and  sulphur  in  the  iron  are 
not  attacked.  It  must  be  borne  in  mind,  however,  that  the  readi- 
ness with  which  carbon  reacts  is  largely  a  function  of  its  physical 


126  INDUSTRIAL  HYDROGEN 

state.  It  has  been  noted,  in  the  discussion  of  the  steam-iron  proc- 
ess, that,  with  progressive  use  of  the  iron  contact  mass,  the  car- 
bon content  of  the  hydrogen  increases,  due  to  deposition  of  ac- 
tive carbon  in  the  iron.  It  is  possible  that  in  the  regeneration 
process  necessary  in  this  method  of  hydrogen  production,  carbon 
of  a  more  reactive  nature  might  well  become  associated  with  the 
iron.  In  such  case,  an  increase  of  impurities  would  make  itself 
evident.  Owing,  however,  to  the  low  reaction  temperature,  it  fol- 
lows that  the  carbon  monoxide  percentage  would  always  be  low 
as  compared  with  that  of  carbon  dioxide,  owing  to  the  operation 
of  the  water-gas  reaction, 

H20  +  CO  =  H2  +  C02, 

as  in  the  steam-iron  and  water-gas  catalytic  processes.  Sabatier 
has  shown  that  a  reactive  carbon  produced  catalytically  may  re- 
act with  steam  to  give  methane.3  In  this  way  the  saturated  hy- 
drocarbons may  accumulate  in  the  hydrogen  produced. 

General  Discussion. — The  general  features  of  the  process  are 
such  that  it  should  lend  itself  especially  to  hydrogen  generation 
where  low  plant  cost,  intermittency  of  use,  simplicity  of  opera- 
tion and  compactness  of  plant  are  desirable.  Hence  it  would 
seem  to  have  distinct  possibilities  in  field  work  and  in  the  gen- 
eration of  hydrogen  at  re-charging  stations  for  dirigible  airships. 
The  writer  has  in  mind  a  source  of  finely  divided  iron  from  which 
it  might  be  possible  to  obtain  the  necessary  supplies  sufficiently 
cheaply  to  permit  of  rejection  of  the  material  after  it  had  passed 
through  the  oxidation  process.  The  sand  used  for  grinding  plate 
glass  contains  a  marked  percentage  of  finely  divided  iron  which 
can  be  extracted  from  the  sand  by  electro-magnetic  means.  Such 
material  should  be  eminently  suitable  for  the  Bergius  process; 
and  the  economy  of  its  recovery  from  sand  would  determine  the 
policy  adopted  in  respect  to  regeneration. 

For  industrial  purposes,  the  utility  of  the  process  appears,  as 
yet,  to  be  limited  to  such  applications  as  involve  the  use  of  highly 
compressed  hydrogen,  as,  for  example,  in  ammonia  synthesis. 
In  this  application,  moreover,  the  present  intermittent  nature  of 
the  process  constitutes  a  point  of  objection.  It  would  undoubt- 
edly entail  a  rather  severe  operational  and  repair  charge.  It  is 
conceivable,  however,  that  technical  development  might  succeed 

•  French  patent  355,900/1905. 


HYDROGEN  FROM  WATER  127 

in  making  the  process  a  continuous  one.  To  this  end,  attention 
should  be  given  more  closely  to  the  original  suggestion  of  Bergius 
in  which  carbon  was  the  agent  used  for  decomposition  of  the 
water.  A  form  of  carbon  as  reactive  as  that  of  iron  would  have 
the  advantage  that  there  would  be  no  residue  resulting  and  re- 
quiring regeneration.  On  the  other  hand  the  hydrogen  produced 
would  require  purification  from  carbon  dioxide  and  probably 
from  carbon  monoxide  for  purposes  of  ammonia  synthesis.  The 
balance  of  advantages  against  disadvantages  offers  an  attractive 
field  for  further  investigative  work. 

Field  Processes 

Certain  processes  have  been  developed  for  the  production  of 
hydrogen  in  the  field  using  water  as  the  source  of  hydrogen. 
The  advantage  sought  in  such  developments  is  the  lessening  of 
the  material  weight,  per  unit  of  hydrogen  produced,  required  to 
be  transported  to  the  scene  of  military  operations.  In  such  proc- 
esses the  material  transported  will  readily  react  with  water  which 
is  generally  available  in  quantity  even  under  service  conditions. 
A  number  of  such  materials  have  now  been  employed.  The  alkali 
metals  have  not  found  extended  use  probably  owing  to  the  dan- 
gers attending  their  transport.  Use  has  been  made,  however,  of 
calcium  in  the  form  of  its  hydride,  the  process  being  known  as 
the  Hydrolith  process.  Activated  aluminium,  or  aluminium  amal- 
gam reacts  readily  with  water  to  form  hydrogen,  and  certain 
aluminium  alloys  may  be  substituted  for  aluminium  in  the  actual 
process.  More  recently,  lead-magnesium  and  lead-sodium  alloys 
have  been  proposed. 

Metallic  Sodium  Processes 

Sodium  in  the  form  of  small  pieces  was  proposed  by  Foerster- 
ling  and  Phillipp 4  for  the  production  of  hydrogen;  the  violence 
of  the  reaction  was  to  be  diminished  by  using  water  in  the  form 
of  a  fine  spray.  A  later  patent  to  Brindley  5  incorporates  the  so- 
dium in  briquettes  compounded  of  the  element  with  crude  oil, 
kieselguhr,  and  aluminium  or  silicon.  In  this  way,  hydrogen  was 
to  be  secured  by  interaction  of  sodium  with  water,  and  the  re- 

•U.  S.  P.  883.531/1908. 
•U.   S.   P.   909,536/1909. 


128  INDUSTRIAL  HYDROGEN 

suiting  alkaline  liquor  was  to  be  used  for  the  generation  of  hy- 
drogen from  the  aluminium  or  silicon  (see  pp.  131-141).  A  sub- 
sequent patent6  utilises  the  same  idea,  by  incorporation  in  the 
briquettes  of  aluminium  silicide. 

The  Hydrolith  Process 

Instead  of  employing  metallic  calcium  in  suitable  form,  Jau- 
bert  proposed,7  for  purposes  of  field  production  of  hydrogen,  the 
use  of  calcium  hydride.  The  earlier  French  patent  deals  with 
the  production  of  this  compound  from  metallic  calcium  and  hy- 
drogen, for  example  from  the  waste  hydrogen  of  electrolytic  alkali 
processes.  Interaction  occurs  readily  at  600°  C.  between  the 
metal  and  hydrogen  freed  from  all  traces  of  oxygen  and  water 
vapor.  The  product  reacts  with  water  in  the  sense  of  the  equa- 
tion 

CaH2  +  2H20  =  Ca(OH)2  +  2H2. 

The  commercial  product,  which  is  a  white  crystalline  powder, 
containing  about  90  per  cent  calcium  hydride  together  with  some 
nitride  and  oxide,  yields,  on  treatment  with  water,  upwards  of 
34,000  cubic  feet  per  ton.  Hence,  the  weight  involved  in  the 
transportation  of  material  sufficient  to  produce  1 ,000  cubic  feet  of 
hydrogen  is  less  than  65  pounds.  Its  applicability  for  field  pur- 
poses is  thus  manifest.  Portable  units  with  a  total  capacity  of 
700,000  cubic  feet  of  hydrogen  have  yielded  satisfactory  results 
when  tested  by  the  French  in  actual  field  conditions. 

The  generators  contain  calcium  hydride  in  a  series  of  open 
work  trays.  Water  is  admitted  from  below  and  the  hydrogen 
passes  away  from  the  top  of  the  generator.  The  reaction  is 
markedly  exothermic  and  moisture  is  freely  carried  away  by  the 
evolved  gas.  This  moisture  is  removed  in  a  convenient  manner  by 
allowing  the  hydrogen  generated  in  the  first  vessel  to  pass  through 
a  second  generator  also  filled  with  calcium  hydride.  In  this  gen- 
erator the  water  vapor  reacts  with  calcium  hydride  liberating 
an  additional  quantity  of  hydrogen.  The  calcium  nitride  present 
as  impurity  in  the  reaction  material  interacts  with  water  to  form 
ammonia.  This  must  be  removed  before  use,  the  removal  being 
readily  accomplished  by  washing  the  gas  counter-current  with 
water  in  a  scrubber. 

•U.    S.   P.   977,442/1910. 

7  P.  P.  327,878/1902  ;  B.  P.  25,215/1907. 


HYDROGEN  FROM  WATER  129 

A  German  modification8  of  the  Jaubert  process  uses  water 
present  in  the  combined  state  in  such  substances  as  gypsum  and 
sodium  bicarbonate.  In  such  cases  reaction  only  occurs  above 
80°  C. 

Aluminium  Amalgam  Processes 

Aluminium  amalgam  reacts  with  water  at  ordinary  tempera- 
tures to  yield  hydrogen,  the  aluminium  being  converted  to  oxide 
and  the  mercury  being  regenerated  in  the  elementary  state 

Al2Hgy  +  3H20  =  A1203  +  3H2  +  yHg. 

Since  the  mercury  thus  formed  may  amalgamate  with  further 
quantities  of  aluminium  and  the  process  be  repeated,  the  mer- 
cury acts  as  a  catalytic  agent  and  can  be  employed  in  very  small 
amount  in  comparison  with  the  aluminium  brought  to  reaction. 
Furthermore,  since  amalgamation  may  be  produced  by  direct  re- 
action between  aluminium  and  mercury  salts  in  solution,  the  mer- 
cury required  for  the  process  may  be  supplied  in  the  form  of  the 
oxide  or  a  salt,  for  example,  the  chloride.  As  a  result,  the  pro- 
duction of  hydrogen  in  the  field  by  this  process  can  be  accom- 
plished with  the  transportation  of  little  more  than  the  aluminium 
requisite  for  the  hydrogen.  The  proportions  of  the  other  con- 
stituents of  the  active  mixture  are  of  the  order  of  1-2  per  cent 
by  weight  of  the  aluminium.  The  proposals  for  the  utilisation  of 
the  aluminium  amalgam  process  are  embodied  in  a  series  of  patent 
specifications  and  in  literature  references  to  the  same.  Mauri- 
cheau  Beaupre  demonstrated  9  that  aluminium  filings,  when  im- 
mersed in  an  aqueous  solution  containing  1-2  per  cent  of  mer- 
curic chloride  and  0.5-1  per  cent  of  potassium  cyanide,  gave  a 
steady  evolution  of  hydrogen.  The  heat  evolved  in  the  reaction 
caused  a  rise  in  temperature  of  the  solution  which  could,  how- 
ever, be  maintained  below  70°  C.  by  the  addition  of  cold  water. 
It  was  shown  that,  from  one  kilogram  of  aluminium,  1,300  litres 
of  hydrogen  could  be  obtained,  which  is  equivalent  to  41,000 
cubic  feet  per  ton  of  2,000  pounds.  The  apparent  density  of  the 
material  used  was  low,  being  approximately  1.36,  so  that  from 
one  litre  of  aluminium  powder  1,700  litres  of  hydrogen  could 
be  produced.  The  process  based  on  these  observations  was  pat-> 

•  D.  R.  P.  218,257/1908. 

•  Compt.  rend.,  1908,  147,  310, 


130  INDUSTRIAL  HYDROGEN 

ented  in  1908,10  a  mixture  being  employed  consisting  of  aluminium 
in  suitable  form,  admixed  with  the  stated  amounts  of  mercuric 
chloride  and  potassium  cyanide.  The  material  is  stable  in  ab- 
sence of  air  and  moisture.  The  water  required  amounts  to  200 
gallons  per  ton  of  mixture. 

According  to  the  patent  claims 11  of  the  Chemische  Fabrik 
Griesheim-Elektron,  aluminium  powder  admixed  with  1  per  cent 
of  mercuric  oxide  and  1  per  cent  of  sodium  hydroxide  is  equally 
efficient  as  a  source  of  hydrogen  and  is  less  poisonous  than  the 
preparations  previously  specified.  In  place  of  sodium  hydroxide, 
salts  having  an  alkaline  reaction  may  be  substituted.12  The 
aluminium  may  be  alloyed  with  other  elements  notably  tin  and 
zinc.13 

The  activity  of  aluminium  alloys  has  been  studied  by  Kohn 
Abrest14  who  established  the  negatively  catalytic  effect  of  cop- 
per on  the  process.  It  was  shown  that  aluminium  containing  0.4 
per  cent  copper  is  not  activated  by  immersion  in  1  per  cent  mer- 
curic chloride  solutions.  As  little  as  0.1  per  cent  copper  was 
found  to  make  the  aluminium  indifferent  towards  water.15  Kohn 
Abrest  also  concludes  that  a  mixture  of  hydroxides  of  aluminium 
is  produced  on  reaction  with  water,  the  composition  varying  ac- 
cording to  conditions,  such  as  the  duration  of  oxidation,  concen- 
tration and  temperature  of  the  solution. 

10  Fr.  pat.  392,725/1908. 

»B.  P.  3,188/1909. 

"Sarason,  B.  P.  18,772/1911. 

"Uyeno.   B.   P.   11,838/1912. 

"  Butt.  8oc.  CMm.,  1912,  1 1,  570.    J.  Ch&m.  Soc.,'  1912,  102  II,  768. 

»  Cwpt.  rend.,  1912,  15k,  1,600. 


Chapter  VII. 
Hydrogen  From  Aqueous  Alkalis. 

The  Silicol  Process 

Hydrogen  for  filling  military  and  naval  dirigibles  or  balloons 
has  been  extensively  produced  in  recent  years  by  the  action  of 
aqueous  alkalis,  especially  sodium  hydroxide,  on  silicon,  generally 
in  the  form  of  ferro-silicon.  The  method  is  expensive  owing  to 
the  high  cost  of  raw  materials.  As  the  hydrogen  may  be  pro- 
duced, however,  at  a  very  rapid  rate,  of  high  purity,  in  a  small, 
compact  and  inexpensive  plant,  with  low  labor  and  power  require- 
ments, the  process  is  eminently  adapted  to  field  purposes  and  for 
the  inflation  of  lighter-than-air  craft  aboard  ship  at  sea. 

Outline  of  the  Process. — The  operations  involved  in  the  proc- 
ess are  (1)  the  preparation  of  the  solution  of  sodium  hydroxide 
(2)  the  admixture  of  ferro-silicon  with  the  alkaline  solution  (3) 
the  separation  of  water  vapor  from  the  hydrogen  evolved  in  the 
interaction.  For  these  operations,  the  essential  plant  required 
consists  of  a  solution  tank  in  which  the  sodium  hydroxide  is 
dissolved,  a  generator  in  which  the  reaction  takes  place  and  a 
condenser  or  cooler  in  which  the  gas  generated  is  freed  from 
water  vapor  simultaneously  evolved  from  the  reaction  mixture 
owing  to  the  temperature  at  which  the  reaction  occurs.  This  tem- 
perature of  reaction  is  maintained  by  means  of  the  two  proc- 
esses occurring,  the  solution  of  sodium  hydroxide,  in  which  suffi- 
cient heat  is  produced  to  start  the  reaction,  and  the  hydrogen 
generation,  which  is  so  strongly  exothermic  that  careful  control 
of  the  temperature  is  necessary. 

From  one  gram  atom  of  silicon,  four  gram  atoms  of  hydrogen 
may  be  theoretically  produced.  Less  sodium  hydroxide  is  re- 
quired than  that  corresponding  to  the  equation, 

2NaOH  +  Si  +  H20  =  Na2Si03  +  2H2. 

The  hydrolytic  dissociation  of  sodium  silicate  solutions  would  ac- 
count for  such  an  observation,  or,  alternatively,  the  silicate 

131 


132  INDUSTRIAL  HYDROGEN 

formed  may  be  more  complex,  as  for  example  that  given  in  the 
equation, 

2NaOH  +  2Si  +  3H20  —  Na2Si205  +  4H2. 

Literature  Resume. — The  use  of  silicon  with  caustic  soda  solu- 
tions for  hydrogen  generation  is  claimed  in  the  patent  applica- 
tion of  the  Consortium  fiir  Elektrochemische  Industrie,  G.  m.  b. 
H.1  Milk  of  lime  may  be  added,  it  is  claimed,  to  reduce  the 
amount  of  caustic  soda  required.  A  patent2  to  the  same  firm 
claims  the  elimination  of  the  necessity  for  external  heat  by  pre- 
liminary interaction  of  the  sodium  hydroxide  solution  with  alu- 
minium or  by  the  production  of  a  hot  sodium  hydroxide  solution, 
by  adding  the  alkali  to  the  water  in  the  powdered  form.  This 
use  of  silicon  and  hot  soda  solutions  has  been  developed  mainly 
in  Germany  for  field  purposes  under  the  name  of  the  Schuckert 
process.  French,  British  and  American  plants  have  employed  the 
cheaper  ferro-silicon,  this  development  being  largely  due  to  Jau- 
bert,  the  French  chemist,  and  the  Societe  Franchise  L'Oxylithe.3 

Experimental  Data. — An  intensive  study  of  the  governing 
factors  in  the  operation  of  the  process  for  military  purposes  has 
been  made  by  the  U.  S.  Bureau  of  Standards.  A  paper  by 
Weaver  4  presents  the  method  of  investigation  employed  and  an 
analysis  of  the  factors  of  importance,  which  will  be  reproduced 
briefly  in  the  following.  The  reaction  occurs  at  the  surface  of 
contact  of  the  ferro-silicon  and  the  solution.  With  the  solid  com- 
pletely wetted,  the  rate  of  reaction  is  dependent  on  the  amount 
of  surface  of  the  ferro-silicon,  the  composition  of  the  liquid  and 
the  solid  phase,  and  on  the  temperature.  In  addition  to  rate 
of  reaction,  the  hydrogen  yield  from  unit  weight  of  silicon  is  of 
first  importance. 

The  yield  of  hydrogen  in  practice  is  by  no  means  independent 
of  the  silicon  content  of  the  ferro-silicon  as  it  should  be  upon 
theoretical  grounds.  Thus,  as  is  shown  in  the  appended  figure, 
Fig.  XIII,  the  hydrogen  yield  under  the  conditions  most  favor- 
able for  obtaining  a  complete  reaction  only  approaches  theoreti- 

JB.  P.  21,032/1909. 
»B.  P.  11,640/1911. 

•Jaubert,   F.    P.,    430,302/1910;    B.    P.    17,589/1911;    P.    P.,    433,400/1913; 
B.  P.  7,494/1913.     U.  S.  P.   1,037,919. 
««/.  Ind.  Eng.  Ghent.,  1920,  12,  232. 


HYDROGEN  FROM  AQUEOUS  ALKALIS 


133 


cal  efficiency  with  ferro-silicon  containing  upwards  of  80  per 
cent  silicon.  Furthermore,  the  initial  rate  of  reaction  attains  a 
maximum  with  ferro-silicon  of  about  90  per  cent  silicon  content. 
Also,  the  rate  of  evolution  of  hydrogen  expressed  as  a  percentage 
of  the  initial  rate  falls  away  linearly  with  increasing  percentage 
of  total  silicon  consumed  in  a  given  trial.  All  these  experi- 
mental facts  point  to  the  advantage  of  employing  a  ferro-silicon 
containing  in  the  neighbourhood  of  90  per  cent  silicon. 

Ferro-silicon  of  the  same  composition  gives  the  same  total 


^^ 

r 


IF 
h 


4i 


4 


fte/af/o/7  of 


O          £0         40         60         00         /00X 

<S///co/?  /n  ferrosf/icon 

FIG.  XIII.     Relation  of  Silicon  content  to  Hydrogen  Yield. 

yield  of  hydrogen  under  the  most  favorable  circumstances  in- 
dependently of  its  state  of  division.  A  material  of  finer  subdi- 
vision, however,  gives  a  more  rapid  evolution  of  hydrogen  in 
the  earlier  stages  of  the  process  than  the  coarser  material. 

The  concentration  of  the  sodium  hydroxide  solution  is  a  very 
important  factor.  With  increasing  concentration  of  solution  the 
initial  rate  of  reaction  increases  steadily.  The  effect  of  dilu- 
tion, however,  is  dependent  on  the  amount  of  silicon  which  has 
already  been  dissolved  in  the  soda  solution.  Thus,  the  rate  of  so- 
lution of  ferro-silicon  in  a  20  per  cent  sodium  hydroxide  solu- 
tion containing  no  dissolved  silicon  is  quite  different  from  that 
in  a  solution  which  is  20  per  cent  with  regard  to  free  alkali  but 


134 


INDUSTRIAL  HYDROGEN 


which  also  contains  sodium  silicate  from  previous  reaction.  Dis- 
solved silicon  depresses  the  rate  of  reaction. 

The  total  yield  is  also  affected  by  the  concentration  of  alkali. 
With  solutions  which  are  too  dilute,  the  yield  of  hydrogen  is 
poor.  Also,  there  is  a  greater  tendency  to  "frothing."  The  froth- 
ing may  be  so  great  as  to  carry  liquid  out  of  the  generator  into 
the  pipes  and  valve  systems  causing  blocks  and  stoppages.  Solu- 
tions of  high  alkali  concentrations,  on  the  other  hand,  while  giv- 
ing rapid  gas  evolution,  produce  highly  viscous  fluids  which  may 
cause  considerable  trouble  in  removal  from  the  generator  sys- 
tem and  result  also  in  poor  hydrogen  yields,  due  to  incomplete 
reaction  of  the  ferro-silicon  in  the  viscous  mass. 

The  following  table  given  by  Teed 5  represents  results  ob- 
tained with  a  ferro-silicon  containing  92  per  cent  silicon  and  a 
98  per  cent  sodium  hydroxide  as  raw  materials.  The  figures 
include  data  from  solutions  more  dilute  and  more  concentrated 
than  the  25  per  cent  solution,  which  is  the  concentration  obtain- 
ing in  average  practice. 


Concentration  of  So- 
dium Hydroxide  So- 
lution 

Ratio  of  Silicon  to 
Sodium  Hydroxide 

Hydrogen  Yield  in 
Cubic  Feet  per  Lb. 
of  Silicol 

10  per  cent 

1  :  0.745 

13.62 

10 

1  :  1.065 

14.30 

10 

1  :  1.480 

15.36 

10 

1  :  3.20 

16.80 

30 

1  :  0.852 

19.35 

30 

1  :  2.13 

23.90 

30 

1  :  3.19 

23.58 

40 

1  :  1.58 

24.10 

40 

1  :  3.19 

24.50 

The  hydrogen  yield  is  expressed  at  a  pressure  of  30  inches  of 
mercury  and  a  temperature  of  60°  F.  The  maximum  possible 
yield  under  these  conditions  would  be  25.4  cubic  feet  per  pound 
of  silicol  of  the  stated  purity. 

Temperature  increases  the  rate  of  hydrogen  evolution.  An 
increase  of  reaction  temperature  from  100  to  110°  C.  increases 

•  Chemistry  and  Manufacture  of  Hydrogen,  Arnold,  1919,  p.  53. 


HYDROGEN  FROM  AQUEOUS  ALKALIS 


135 


the  reaction  velocity  by  50  per  cent.  At  90°  C.  the  rate  ii  ap- 
proximately 68  per  cent  of  that  at  100°  C.  With  a  reaction  tem- 
perature in  this  neighbourhood  it  is  obvious  that  the  hydrogen 
evolved  will  contain  a  considerable  concentration  of  water  vapor 
corresponding  with  the  vapor  pressure  of  the  solution  at  the 
given  temperature.  It  is  this  factor  of  water  evaporation  which 
necessitates  the  employment  of  alkali  solutions  of  medium  con- 
centrations and  the  addition  of  water  to  cool  and  dilute  the  solu- 
tion. This  factor  of  vaporisation  and  the  heat  required  to  effect 


so 


<<. 


^ 


faafofY0/w/z0ffort  /s  eyva/ 
fo  heaf  0f  reaction 


60 


7O 


Concentration  ofo/Aa//  so/ut/on 

of  NaOli  per  /OO  yra/ns  of  water) 

FIG.  XIV.     Heat  of  Vaporisation  Data. 


the  same  constitutes  one  of  the  important  safeguards  in  this 
process,  as  preventing  the  attainment  of  excessive  tempera- 
tures. Ample  body  of  solution  should  always  be  assured.  The 
accompanying  diagram,  Fig.  ~X.IV  shows  the  temperature  at  which 
heat  of  vaporisation  is  equal  to  heat  of  reaction  for  various 
barometric  pressures  and  different  alkali  concentrations,  the  heat 
of  reaction  being  assumed  to  be  49  Kilogram  calories  per  gram 
molecule  of  silicon  dissolved  in  the  alkali. 


136 


INDUSTRIAL  HYDROGEN 


The  application  of  such  experimental  data  to  the  actual  work- 
ing operation  has  been  illustrated  by  Weaver 6  in  a  series  of  gen- 
erator problems.  The  accompanying  figure,  Fig.  XV,  collects  the 


Vapor  Pressure       /so 
rerros/'//con  /trfs&rt  o 


f/rrpera/t/re  so 

ftafe  pas  era/of /b/7  -o 
Tafo/  gas  ero/rtef     0 


SO 
XT 
/SO 


/0O 

2? 


30 
//<?'  C 

jo  ct/,  mgfers  permit?. 


/f~r/-0s///'c0/T 
/eea{ 


FIG.   XV.     Graphical   Representation   of   Generator   Problem. 


results  of  such  an  investigation  in  graphical  form.  The  data 
apply  to  a  generator  in  the  form  of  an  unprotected  cylindrical 
tank  6  feet  6  inches  high  and  6  feet  in  diameter,  made  of  one- 
quarter  inch  boiler  plate;  the  solution  tank,  having  about  one- 
fourth  the  capacity  of  the  generator,  is  assumed  to  have  a  heat 
capacity  including  stirring  machinery  equal  to  one-half  of  that 
of  the  generator.  Air  temperature  is  assumed  to  be  20°  C.,  sup- 
ply water  to  be  at  18°  C.,  and  barometric  pressure  740  mm.  of 
mercury.  The  wind  velocity  is  10  miles  per  hour. 

The  charge  is  363  kg.  of  ferro-silicon,  88  per  cent  Si,  of  the 
fineness  given  by  the  following  data: 

Per  Cent 

Rejected  by  20  mesh    10 

Through  20,  on  30    20 

30,    "    40    10 

40,    "    60    10 

50,   "    80    15 

80,    "    100    15 

Through  100 20 


Total 

•Loc.  cit.  235-237. 


100  per  cent 


HYDROGEN  FROM  AQUEOUS  ALKALIS          137 

Generation  is  started  with  a  30  per  cent  solution  of  sodium 
hydroxide  made  by  dissolving  290  kg.  of  alkali  in  677  kg.  of 
water.  In  order  to  heat  the  solution  more  quickly  only  half  the 
solution  and  75  pounds  of  ferro-silicon  are  introduced  into  the 
generator.  When  the  temperature  reaches  90°  C.  the  ferro-silicon 
feed  is  started  at  the  uniform  rate  of  15  pounds  per  minute  and 
continued  until  all  the  charge  has  been  added.  As  soon  as  the 
ferro-silicon  feed  is  started,  the  remainder  of  the  solution  is  run 
into  the  generator  at  such  a  rate  as  to  keep  the  temperature  con- 
stant. When  all  the  solution  has  been  added  the  constant  tem- 
perature is  maintained  by  the  addition  of  cold  water  until  the 
solution  contains  about  20  per  cent  of  sodium  hydroxide.  The 
water  is  then  stopped  and  no  further  effort  made  to  control  the 
reaction. 

For  the  method  of  obtaining  such  a  chart  and  for  the  data 
which  are  employed  in  computing  the  same,  the  original  article 
should  be  consulted.  A  discussion  of  the  accuracy  and  signifi- 
cance of  such  generator  calculations  is  also  given. 

Weaver  concludes  that  in  spite  of  the  many  conditions  af- 
fecting the  rate  of  reaction  of  a  given  amount  of  ferro-silicon, 
the  rate  of  evolution  of  gas  over  the  major  part  of  a  generator 
run  is  primarily  a  function  of  the  rate  of  addition  of  ferro-silicon. 
With  varying  conditions  of  temperature  and  concentration  of 
solution,  provided  these  are  reasonably  constant,  the  ferro-sili- 
con feed,  if  regular,  will  cause  accumulation  of  material  in  the 
generator  until  the  amount  of  reacting  surface  is  such  that  the 
rate  of  solution  will  approximate  the  rate  of  addition.  Conditions 
must  be  so  chosen  that  equilibrium  is  quickly  reached  without 
generating  gas  at  an  excessive  rate;  there  should  be  no  sudden  va- 
riations of  generator  conditions,  particularly  of  temperature;  the 
reaction  should  also  come  quickly  to  an  end  after  the  ferro-silicon 
is  all  exhausted.  The  procedure,  outlined  in  the  generator  prob- 
lem cited,  as  to  the  start  of  the  reaction  is  probably  the  best 
for  bringing  the  generator  temperature  rapidly  to  the  working 
equilibrium.  Fig.  XIV,  shows  the  temperatures  at  which  the 
heat  of  vaporisation  of  the  water  carried  away  by  the  gas  at 
various  concentrations  of  alkali  will  be  equal  to  the  heat  of  re- 
action. These  represent  the  maximum  temperatures  beyond 


138        .  INDUSTRIAL  HYDROGEN 

which  the  generator  could  not  rise  if  there  were  no  other  heat 
losses  than  through  evaporation.  In  actual  practice  these  tem- 
peratures will  be  approached  more  or  less  closely  depending  on 
the  magnitude  of  the  other  heat  losses,  which  vary  with  the 
atmospheric  conditions  and  with  the  position  of  a  plant,  whether 
housed  or  in  the  field.  The  initial  charge  of  ferro-silicon  added 
to  the  solution  or  portion  theroof  should  be  of  such  a  size  that 
when  the  desired  generator  .temperature  is  reached  the  rate  of 
reaction  will  be  the  desired  average  for  the  run.  If  the  tempera- 
ture of  the  alkali  be  initially  low  it  is  advisable  to  add  the  neces- 
sary ferro-silicon  in  the  finely  divided,  more  rapidly  reacting 
form.  Aluminium  is  sometimes  used  as  a  substitute  for  such  finely 
powdered  or  high  grade  ferro-silicon  to  attain  the  initial  reaction 
temperature. 

Weaver  shows  that,  for  a  20  per  cent  alkali  solution  the  yield 
of  hydrogen  during  a  one  hour  run  increases  with  increasing 
ratio  of  sodium  hydroxide  to  silicon  and  attains  a  figure  beyond 
which  increase  of  alkali  is  of  negligible  effect.  From  such  data, 
assuming  cost  figures  of  12.5^  and  6^  per  Ib.  for  ferro-silicon  and 
sodium  hydroxide  respectively,  it  is  calculated  that  the  greatest 
economy  is  obtained  by  using  about  seven-tenths  as  much  sodium 
hydroxide  as  silicon  present  in  the  material.  Use  of  equal  weights 
of  both,  however,  decreases  the  danger  of  obtaining  viscous  solu- 
tions at  the  end  of  a  run.  On  the  other  hand,  according  to  Weaver, 
it  costs  more  to  produce  a  given  volume  of  hydrogen  when  too 
little  sodium  hydroxide  is  used,  only  because  ferro-silicon  remains 
unacted  upon  at  the  end  of  the  run.  The  amount  of  material 
wasted  decreases  very  rapidly  when  generation  is  permitted  to 
proceed  for  a  short  time  after  the  material  is  added ;  hence  when 
haste  is  not  an  important  object  greater  economy  could  no  doubt 
be  secured  by  using  a  still  smaller  proportion  of  alkali.  These 
conclusions  of  Weaver  conflict  with  those  of  Teed  who  advises  a 
ratio  of  silicon  to  sodium  hydroxide  as  high  as  1  to  1.72.7  Amer- 
ican practice  represents  the  conclusions  of  more  recent  work  and 
is  certainly  the  more  economical. 

The  patent  to  the  Compagnie  Generale  d'  Electrochimie  de 
Bozel 8  suggests  economy  in  the  matter  of  sodium  hydroxide  by 
the  use  of  a  lime-sodium  carbonate  mixture.  As  an  example,  a 

7  Cf.  also  British  Admiralty  Hydrogen  Manual,  Vol.  I,  p.  137. 
8B.  P.  127,018/1917. 


HYDROGEN  FROM  AQUEOUS  ALKALIS          139 

mixture  of  silicon  20  parts,  lime  80  parts,  sodium  carbonate  10 
parts,  and  water  225  parts  is  cited.  The  matter  of  using  lime  has 
been  investigated  experimentally  by  Gordon.9  He  found  that  it 
was  impracticable  to  substitute  lime  for  sodium  hydroxide  en- 
tirely, as  the  rate  of  reaction  is  so  slow  due  to  the  low  alkali  con- 
centration of  the  saturated  solution  of  lime.  It  was  also  shown 
that  the  recovery  of  sodium  hydroxide  from  generator  sludge  by 
addition  of  lime  was  impracticable  as,  even  with  careful  treat- 
ment, it  is  difficult  to  recover  even  50  per  cent  of  the  original 
alkali.  Owing  to  the  voluminous  nature  of  the  precipitate  of  cal- 
cium silicate,  the  recovery  of  the  alkali  would  require  the  use  of 
filter  presses.  For  operations  in  the  field,  this  necessity  would 
diminish  the  value  of  the  process  with  respect  to  smallness  and 
compactness  of  plant.  On  the  large  scale,  with  stationary  plant 
and  large  alkali  consumption,  use  of  a  filter  press  would  undoubt- 
edly effect  economies.  Using  lime  and  sodium  carbonate  in  place 
of  sodium  hydroxide  was  found  by  Gordon  to  be  possible.  With 
even  a  larger  excess  of  alkali  (as  sodium  carbonate-lime),  how- 
ever, the  yield  of  hydrogen  was  only  89  per  cent  of  that  from 
sodium  hydroxide  solutions  in  excess.  Also,  the  effect  of  reducing 
the  ratio  of  alkali  to  ferro-silicon  is  very  marked  and  is  much 
greater  than  when  pure  sodium  hydroxide  is  used.  Rate  of 
hydrogen  evolution  was  also  slower  and  a  large  excess  of  lime 
proved  to  be  a  marked  detriment.  A  solution  equivalent  to  12.5 
per  cent  sodium  hydroxide  was  somewhat  better  than  a  10  per 
cent  solution  and  very  considerably  better  than  a  20  per  cent 
solution. 

Plant  Details.— Plants  generating  between  1,500  and  60,000 
cubic  feet  of  hydrogen  per  hour  have  been  built  and  operated  in 
the  last  few  years  in  the  various  allied  countries.  While  alike  in 
essentials  the  various  sizes  differ  in  detail,  for  example,  in  con- 
denser equipment,  source  of  necessary  power,  mechanism  of  sili- 
col  feed  and  of  temperature  control. 

The  necessary  parts  in  all  plants  include  the  following: 

(1)  A  caustic  soda  vat,  in  which  the  alkali  is  dissolved,  fitted 
with  stirring  mechanism. 

(2)  A  generating  tank,  in  which  the  reaction  occurs,  fitted 
with  stirring  mechanism. 

•  U.  S.  National  Advisory  Committee  for  Aeronautics,  Report  No.  40. 


140  INDUSTRIAL  HYDROGEN 

(3)  A  hopper,  to  hold  the  powdered  ferro-silicon,  and  fitted 
with  suitable  adjustable  feeding  device. 

(4)  A  cooling  chamber  in  which  moisture  is  separated  from 
the  hot  hydrogen. 

(5)  A  condenser  system  in  which  the  gas  is  washed  and  cooled. 

(6)  A  power  plant  to  operate  stirrers,  pumps,  etc.     In  the 
smaller  plants  the  necessary  power  is  supplied  by  hand. 

Generators. — These  are  usually  cylindrical  tanks  but  in  the 
smaller  units  may  be  rectangular.  A  tank  having  a  hydrogen 
capacity  of  10,000  cubic  feet  per  hour  will  average  about  5  feet 
in  diameter  by  9  feet  deep  or  a  wider,  shallower  cylindrical  ves- 
sel of  the  same  cubical  capacity.  The  dimensions  of  a  unit  pro- 
ducing 60,000  cubic  feet  per  hour  will  be  as  much  as  9  feet  in 
diameter  and  12  feet  high  or  its  equivalent  in  cubic  capacity. 
The  tanks  should  be  of  commercial  sheet  steel  of  suitable  size  to 
stand  the  necessary  flanging,  should  be  easily  and  readily  welded. 
All  the  tank  seams  should  be  welded.  On  a  flange  at  the  top 
of  the  generating  tank,  a  cover  held  in  place  by  nuts  and  bolts 
is  made  to  give  a  gas-tight  vessel  with  suitable  gasket  between 
cover  and  flange.  Through  the  cover  passes  a  stirring  gear  for 
the  generator,  driven  by  bevel  gearing  from  a  horizontal  shaft, 
so  driven  as  to  give  60  revolutions  per  minute  to  the  vertical  shaft. 
From  the  base  of  the  tank,  the  sludge  is  discharged  through  a 
4  inch  drain  fitted  with  a  suitable  gate  valve.  A  cold  water 
spray  for  diluting  the  contents  of  the  generator  and  regulating 
its  temperature  is  also  provided. 

The  Ferro-Silicon  Hopper. — This  varies  in  different  plants.  In 
some  the  hopper  is  provided  at  the  top  with  a  self-opening  man 
hole  of  gas-tight  construction  and  an  adjustable  feeding  mechan- 
ism to  feed  dry  silicol,  the  feed  being  variable  between  all  ranges 
of  feed  from  zero  to  maximum  capacity  of  the  generator.  This 
feed  may  be  hand  driven  or  mechanical.  The  British  Admiralty 
adopted  and  standardised  a  wet  feed  process.  The  ferro-silicon, 
in  suspension  in  water,  and  so  maintained  by  mechanical  agita- 
tion, is  fed  into  the  generator  through  a  delivery  pipe  having  a 
jet  feed  the  size  of  which  varies  with  the  capacity  of  the  plant. 
For  a  plant  producing  2,500  cubic  feet  per  hour  two  feeds,  with 
jets,  i/4"  and  5/16"  are  employed.  For  a  unit  with  a  capacity  of 


HYDROGEN  FROM  AQUEOUS  ALKALIS          141 

60,000  cubic  feet  per  hour,  the  maximum  size  of  jet  is  %".  The 
amount  of  silicol  introduced  through  the  jets  is  determined  by  the 
height  of  liquid  above  the  jet  and  the  pressure  of  gas  in  the  gen- 
erator. Both  must  be  kept  under  observation  and  control  to  en- 
sure steady  generation.  Wet  feeds  are  being  studied  in  this 
country  at  the  present  time. 

Soda  Vats. — In  modern  units  these  are  covered  as  with  the 
generator  and  provided  with  similar  stirring  gear  to  facilitate 
rapid  solution  of  the  alkali.  They  are  approximately  about  half 
the  cubic  capacity  of  the  generator. 

Condenser  Equipment. — For  the  separation  of  water  vapor, 
use  is  made  both  of  water  cooling  and  air  cooling.  In  large  sta- 
tionary units  coke  scrubbers  of  the  usual  type  may  be  used.  For 
a  20,000  cubic  feet  per  hour  unit  a  coke  scrubber  5  feet  in  diam- 
eter by  12  feet  high  is  adequate.  In  portable  plants,  the  coke 
may  be  replaced  by  a  series  of  grids  of  light  sheet  steel,  nickel- 
plated  for  protection  against  corrosion.  To  economise  water  in 
portable  plants,  a  supplementary  water  cooler  is  provided  in 
which  the  water  is  allowed  to  flow  over  nickel  plated  cooling  grids 
counter  current  to  a  supply  of  air  coming  from  a  fan.  Single 
stage  circulating  pumps  of  the  centrifugal  type  are  also  pro- 
vided for  water  circulation. 

To  free  the  hydrogen  still  further  from  water  vapor  and  also 
from  entrained  moisture,  the  gas  is  finally  made  to  travel  at  high 
speed  through  a  series  of  tubes  or  passages  having  abrupt  di- 
rectional changes.  In  this  way  hydrogen  of  greater  lifting  power 
for  balloons  is  secured. 

Power  Equipment. — For  small  units,  hand  power  alone  is  nec- 
essary. For  larger  units,  gasolene  or  oil  engines  or  electric  drive 
has  been  provided.  A  5  h.  p.  oil  engine  is  adequate  for  a  10,000 
cubic  feet  plant  of  the  stationary  type.  For  a  unit  of  hourly 
capacity  equal  to  20,000  cubic  feet,  fitted  with  circulatory  pumps, 
air  fans,  etc.,  a  20  H.  P.  engine  or  motor  of  similar  capacity  has 
been  specified. 

Operational  Details. — Since,  at  starting  up,  the  generator  is 
filled  with  air  the  first  gas  evolved  should  be  blown  to  waste.  If 
the  plant  be  operated  in  conjunction  with  a  gas  holder  the  elim- 


142  INDUSTRIAL  HYDROGEN 

ination  of  air  is  best  accomplished  by  closing  all  valves  but  that 
to  the  sludge  discharge  prior  to  feeding  the  sodium  hydroxide  so- 
lution to  the  generator.  The  whole  system  should  then  be  swept 
out  backwards  from  the  gas  holder  through  to  the  sludge  drain. 
According  to  Weaver,10  with  a  regulated  temperature  of  sodium 
hydroxide  solution  and  fixed  rate  of  silicol  feed  it  is  possible  to 
determine  the  length  of  time  required  for  purging  the  generator 
and  condenser  equipment  by  observing  the  temperature  rise  in 
the  generator.  Data  are  given  to  show  the  method  of  computa- 
tion. It  is  possible  to  check  the  length  of  time  necessary  for 
purging  of  the  system  by  observation  of  the  end  of  the  hydrogen 
pipe  when  the  air  has  been  practically  freed  of  air.  The  difference 
in  light  refraction  of  hydrogen  and  air  makes  the  escaping  hy- 
drogen very  noticeable  to  a  trained  observer. 

To  prevent  foaming  in  the  generator  tank  and  consequent  en- 
trainment  of  reacting  materials  with  the  gas,  use  may  be  made 
of  a  mineral  grease.  In  large  plants  this  is,  however,  generally 
unnecessary.  A  charge  of  mineral  grease  equivalent  to  1  Ib. 
per  1,000  cubic  feet  of  gas  generated  should  be  sufficient.  It  is 
conveniently  introduced  through  the  soda  vat  but  may  be  intro- 
duced through  a  special  device  in  the  generator  cover.  It  should 
be  emphasized  that  non-saponifiable  greases  be  used. 

In  the  plant  all  lead  jointings  should  be  eliminated  owing  to 
the  danger  of  an  explosive  reaction  with  silicon 

Pb304  +  2Si  =  2Si02  +  3Pb. 

• 

Separate  storage  for  ferro-silicon  and  sodium  hydroxide  is 
especially  desirable.  Moist  mixtures  of  the  two  solids  react  most 
energetically  and  may  become  incandescent.  Furthermore,  pro- 
cedure should  be  such  that  it  is  next  to  impossible  for  the  caustic 
liquor  to  reach  a  ferro-silicon  mass.  The  heat  of  reaction  between 
the  two  is  so  great  that  the  ferro-silicon  must  always  be  added 
to  excess  liquor,  never  the  reverse,  liquor  to  excess  ferro-silicon. 

On  completion  of  the  reaction  process,  the  sludge  should  be 
immediately  discharged,  to  obviate  solidification  in  the  generator. 
Hot  water,  for  washing  out  the  sludge,  diminishes  the  tendency 
to  solidification.  The  generator  should  be  thoroughly  washed 
out  with  fresh  water  after  each  run  is  made. 

10Loc.  cit. 


HYDROGEN  FROM  AQUEOUS  ALKALIS          143 

Ferro-Silicon  Specifications. — From  the  discussion  previously 
given  it  is  apparent  that  a  ferro-silicon  containing  not  less  than 
80  per  cent  silicon  should  be  specified.  The  residual  material  is 
principally  iron  and  aluminium  with  small  amounts  of  calcium, 
carbon,  phosphorus  and  arsenic.  Iron  is  generally  assumed  to  be 
an  inert  constituent.  By  some  it  is  regarded  as  a  catalytic  acceler- 
ator of  the  reaction  process.  Others  have  claimed  that  iron  en- 
ters into  the  reaction,  yielding  hydrogen,  but  this  is  doubtful. 
Metallic  aluminium  is  a  useful  constituent  of  the  alloy  since  it 
reacts  with  the  alkali  to  yield  hydrogen.  Phosphorus,  arsenic 
and  calcium  carbide  should  be  maintained  at  as  low  a  figure  as 
possible,  since  they  give  rise  to  acetylene,  phosphine  and  arsine 
in  the  hydrogen  produced,  which  gases  have  a  harmful  effect  on 
the  balloon  fabric  as  well  as  being  poisonous  and  liable  to  pro- 
mote inflammability  in  the  gas. 

A  typical  analysis  of  a  high  grade  ferro-silicon  with  minimum 
and  maximum  specifications  as  required  by  the  British  Admiralty 
is  appended. 

Silicon 90.0  per  cent    Not  less  than  85  per  cent 

Iron 4.5    "      " 

Aluminium   4.6    "      " 

Carbon  (Free)  . .  0.2    "      "        Not  more  than  1.0    per  cent 

Calcium 0.2    "      "        Not  more  than  0.25    "      " 

pS  I 0.02  "      "        Not  more  than  0.05    "      " 

Moisture 0.10  "      "  

Undetermined    . .     0.38  "      " 

The  American  standard  is  80-85%  Si  and  to  pass  through  a 
30  mesh  sieve. 

Composition  of  the  Gas. — The  hydrogen  produced  is  of  very 
high  purity,  the  main  impurities  being  phosphine,  arsine  and  sul- 
phuretted hydrogen  which  result  from  interaction  of  impurities 
in  the  ferro-silicon  with  the  alkaline  liquor.  The  concentration 
of  these  gases  is  extremely  small,  however,  the  phosphine  and  ar- 
sine not  generally  exceeding  0.01  per  cent.  Even  these  conceir 
trations,  however,  tend  to  impair  balloon  fabric  and  attack  cop- 
per or  brass  when  oxygen  is  present.  Aluminium  and  zinc  appear 
to  be  immune  from  such  corrosive  action,  so  that,  taken  in  con- 


144  INDUSTRIAL  HYDROGEN 

junction  with  its  lightness,  aluminium  constitutes  an  ideal  metal 
for  dirigible  structures.  According  to  Jaubert 1X  preliminary  treat- 
ment of  ferro-silicon  with  an  aqueous  liquid,  e.  g.,  water,  tends 
to  decompose  phosphides  and  so  to  eliminate  phosphine  from  the 
hydrogen  produced. 

Chemical  Composition  of  the  Sludge  and  Its  Disposal. — The 
sludge  consists  of  a  solution,  containing,  in  the  main,  sodium  sili- 
cate, which,  owing  to  hydrolysis,  is  strongly  alkaline  and  liable 
to  form  a  gelatinous  mass  due  to  hydrated  silicic  acid.  In  addi- 
tion, there  are  present  the  original  impurities  of  the  sodium  hy- 
droxide, chiefly  sodium  carbonate,  also  those  from  the  ferro- 
silicon,  principally  iron,  iron  oxide  and  sodium  aluminate.  It  may 
be  possible  to  work  up  such  material  in  small  quantities  for  sili- 
cate of  soda.  Frequently,  however,  it  constitutes  a  waste  product 
difficult  to  dispose  of  owing  to  a  relatively  high  alkali  concentra- 
tion. In  washing  away  to  sewage  it  should  be  very  freely  diluted 
with  water.  Non-caustic  residues  obtained  by  using  a  high  con- 
centration alkali  at  the  start  can  be  used  to  a  certain  extent  in  the 
dyeing  and  bleaching  industry.  Caustic  residues  have  a  potential 
value  in  oil  refining  to  produce  a  neutral  oil,  the  foots,  with  their 
content  of  sodium  silicate,  being  the  basis  for  cheap  soaps. 

General  Remarks  on  the  Efficiency  and  the  Economy  of  the 
Process. — The  outstanding  feature  of  the  process  as  to  efficiency 
is  the  rapidity  with  which  hydrogen  can  be  generated  from  a  re- 
stricted space  and  in  a  brief  period  of  time  from  starting  up. 
This  rapidity  of  generation  and  smallness  of  plant  required,  give 
the  process  a  considerable  importance  in  the  field  of  aeronautics 
and  especially  in  military  and  naval  aeronautics  where  intermit- 
tent working  is  frequent  and  great  speed  of  production  often  es- 
sential. The  low  capital  cost  of  a  ferro-silicon  plant  is  an  item 
in  favour  of  the  process  when  the  plant  is  only  to  be  used  inter- 
mittently. Indeed,  the  plant  cost  in  this  process  forms  a  negli- 
gible item  in  comparison  with  the  direct  cost  of  production.  A 
unit  having  a  capacity  of  20,000  cubic  feet  per  hour  can  be  pur- 
chased for  $12,000,  while  it  may  be  housed  for  approximately  one- 
quarter  of  this  cost,  or  an  extra  investment  of  $3,000.  It  is  not 
possible  to  charge  this  investment  on  the  basis  of  hydrogen  pro- 

»  B.  P.  147,519/1920. 


HYDROGEN  FROM  AQUEOUS  ALKALIS  145 

duced  since  such  a  plant  is  generally  only  run  intermittently. 
Reckoning  interest,  depreciation,  taxes  and  insurance  at  25%, 
however,  this  amounts  to  a  daily  capital  charge  of  less  than  $11. 
The  direct  cost  as  to  raw  materials  is  in  sharp  contrast  to 
this.  Since  the  minimum  requirements  of  ferro-silicon  and 
caustic  soda  will  be  50  Ibs.  of  each  respectively  and  since  average 
trade  prices  for  these  materials  when  consumed  in  quantity  are 
not  less  than  $160  and  $40  per  ton  respectively,  it  follows  that 
the  ingredients  costs  per  1,000  cubic  feet  of  gas  are  at  least: 

50  Ibs.   (85%  ferro-silicon)   =  $4.00 
50  Ibs.  caustic  soda  =  $1.00 

or  a  total  ingredients  cost  not  less  than  $5  per  1,000  cubic  feet  of 
gas.  Furthermore,  it  must  be  remembered  that  if  continuous 
supplies  uf  hydrogen  are  to  be  ensured  these  expensive  raw  ma- 
terials must  be  stored  to  some  extent.  The  outlay  involved  in 
such  a  procedure  must  be  added  to  the  capital  cost  of  the  plant. 
It  is  obvious,  therefore,  why,  even  in  plants  of  moderate 
size,  devoted  to  the  generation  of  hydrogen  for  aeronautical  pur- 
poses, the  recent  tendency  has  been  towards  utilising  one  or  other 
of  the  alternative  methods  of  hydrogen  generation  for  the  normal 
requirements  of  the  station,  reserving  the  silicol  plant  for  emer- 
gency purposes.  For  small  and  isolated  air  stations  the  process 
will  continue  to  find  application  because  of  the  simplicity  of  pro- 
cedure and  the  economy  of  plant  outlay.12 

Aluminium- Sodium  Hydroxide  Process. 

The  procedure  detailed  in  reference  to  the  ferro-silicon  proc- 
ess is  adapted  to  the  preparation  of  hydrogen  by  the  interaction 
of  aluminium  and  aqueous  sodium  hydroxide.  The  reaction  may 
be  represented  by  means  of  the  equation 

2A1  +  2NaOH  +  2H20  ==  2NaA102  +  3H2 

although  there  is  the  possibility  of  production  of  aluminates  of 
the  general  type  Na3A103  as  exemplified  in  the  equation 

2A1  +  GNaOH  =  2Na3A103  +  3H2 

In  either  case,  the  hydrogen  yield  per  unit  of  aluminium  is  the 
same  and  amounts  theoretically  to  upwards  of  45,000  cubic  feet 

13  For  further  discussion  of  this  subject  see  Tee<J,  Engineering,  1920,  109,  811. 


146        »  INDUSTRIAL  HYDROGEN 

of  hydrogen  per  ton  of  aluminium.  The  sodium  hydroxide  re- 
quired in  practice  corresponds  more  closely  to  that  required  by 
the  first  equation.  Actual  large  scale  experiments  have  shown 
yields  of  hydrogen  equivalent  to  44,000  cubic  feet  per  ton  of 
aluminium  and  28,000  cubic  feet  per  ton  of  90%  sodium  hydrox- 
ide. This  latter  figure  could  doubtless  be  modified  by  extended 
experiment,  along  the  line  of  Weaver's  investigations  with  ferro- 
silicon,  to  give  a  higher  yield  of  hydrogen  per  unit  of  alkali  used. 

The  aluminium  employed  should  be  in  the  form  of  clippings, 
foil  or  granules.  Massive  metal  is  but  slowly  acted  upon.  Al- 
kali of  the  strength  used  in  the  silicol  process  is  also  applicable  in 
this  process. 

The  sludge  produced  is  more  liquid  than  the  ferro-silicon 
sludge  and  shows  less  tendency  towards  gelatinisation.  It  is  how- 
ever also  strongly  alkaline  since  the  aluminates  are  markedly  hy- 
drolysed.  It  should  be  possible  to  convert  this  sludge  into  market- 
able products  more  easily  than  in  the  case  of  the  silicol  sludge 
since  the  alumina  obtained  by  acidification  of  the  solution  should 
be  suitable  for  use  in  the  preparation  of  aluminium  metal  once 
more. 

The  process  was  used  by  the  Russians  in  the  Russo-Japanese 
war  of  1904;  in  the  recent  war,  the  reaction  was  occasionally 
made  use  of  to  start  the  reaction  in  the  silicol  plants,  since  the 
reaction  with  aluminium  is  more  energetic  at  lower  reaction  tem- 
peratures than  can  be  used  for  the  ferro-silicon  process. 

The  apparatus  employed  in  the  silicol  process  is  directly  ap- 
plicable to  this  process.  The  two  processes  are  so  alike  that  the 
question  of  choice,  once  the  procedure  had  become  standardised 
in  each  case,  would  become  an  economic  one,  dependent  on  the 
relative  costs  of  ferro-silicon  and  aluminium  on  the  one  hand  and 
on  the  potential  market  for  the  alkaline  residue  on  the  other 
hand. 


Chapter  VIII. 
Hydrogen  From  Hydrocarbons. 

The  hydrogen  produced  by  the  various  methods  detailed  in 
the  preceding  chapters  is  obtained  from  water,  which  is  the  cheap- 
est and  most  available  supply  of  combined  hydrogen.    Next  in 
availability  and  the  only  other  naturally  occurring  source  of 
hydrogen  of  considerable  technical  importance  is  the  family  of 
hydrocarbons.    These  hydrocarbons  occur  in  nature  in  the  form 
of  a  complex  mixture  known  by  the  generic  term  of  petroleum, 
generally  in  association  with  the  mixture  of  gaseous  hydrocarbons 
known  as  natural  gas.    The  main  constituents  of  both  petroleum 
and  natural  gas  are  carbon  and  hydrogen,  and  varied  attempts 
have  been  made  to  obtain  from  them  hydrogen,  on  the  one  hand, 
and  either  carbon  or  carbon-containing  gases  on  the  other.    The 
stimulus  to  such  investigations  has  been  twofold;  for,  aside  from 
the  increasing  industrial  importance  of  hydrogen,  the  production 
of  carbon  in  finely  divided  condition  in  a  form  suitable  for  use 
as  a  black  pigment  has  offered  great  possibilities  of  profitable 
application.     The  present  methods  of  producing  carbon  black, 
by  the  incomplete  combustion  of  hydrocarbons,  are  expensive  and 
wasteful  of  a  valuable  raw  material.    Methods  of  producing  car- 
bon black  having  the  necessary  properties  of  such  material,  with 
simultaneous  production  of  hydrogen,  would  inevitably  lead  to 
the  supersession  of  the  old  lamp  black  industry. 

The  process  which  is  utilised  for  the  simultaneous  production 
of  carbon  and  hydrogen  from  hydrocarbons  is  in  all  cases  one  of 
thermal  decomposition.  The  procedure  varies  from  case  to  case 
according  to  the  nature  and  thermal  properties  of  the  hydro- 
carbon to  be  utilised. 

The  data  on  the  stability  of  methane  have  been  critically  ex- 
amined by  Lewis  and  Randall x  who  concluded  that  in  this  case 
they  were  sufficiently  reliable  to  warrant  the  calculation  of  free 
energy  data.  From  the  specific  heats  of  hydrogen  and  methane 

*J.  Am.  Chem.  8oc.f  1915,  37,  467. 

147 


148  INDUSTRIAL  HYDROGEN 

and  the  material  relative  to  heats  of  combustion  of  these  gases 
it  was  deduced  that  the  heat  of  formation  of  methane  from  its 
elements  at  291°  Abs.  was  accompanied  by  the  evolution  of  18,300 
calories,  and  at  0°  Abs.  16,300  calories.  The  free  energy  equa- 
tion hence  derived  was 

PCH, 

AF°  =  -  RTlogeK  ==  -  RTloge  -  -  =  -  16300  +  6.6TlogeT  + 


0.0008T2  -  0.000  000  2  T3  -  26.0  T. 

The  value  for  K  the  equilibrium  constant  thus  derived  shows 
good  agreement  with  the  following  experimentally  determined 
values  of  Mayer  and  Altmayer  2  and  Pring  and  Fairlie.3  It  is 


T°  Abs. 

823 

1473 

1573 

1673 

K== 

0.64 

0.00244 

0.0015 

0.0009 

evident  from  these  figures  that  at  ordinary  temperatures  methane 
is  the  stable  substance;  the  higher  the  temperature,  however,  the 
greater  the  equilibrium  concentration  of  hydrogen  and  the  less 
the  value  for  K. 

This  conclusion  may  be  generalised  by  stating  that  high  tem- 
peratures favour  the  thermal  decomposition  of  exothermic  hydro- 
carbons to  yield  carbon  and  hydrogen. 

In  the  absence  of  similar  critical  data  relative  to  acetylene, 
use  may  be  made  of  the  Nernst  approximation  formula.  The 
exact  magnitude  of  the  thermal  change  accompanying  the  re- 
action is  in  doubt  but  is  of  the  order  indicated  in  the  equation 

C2H2  =  20  +  H2  +  40,000  cals. 
Now,  according  to  the  Nernst  approximation  formula  : 

pC2H2  Q 

logK  =  log  —  ^  =  --  2U  +  2n.  1.75  log  T  +  2nC 

PH2  4-57  a 

where  log  K  applies  to  the  partial  pressures  of  the  gas  ex- 
pressed in  atmospheres  at  a  total  pressure  of  one  atmosphere; 
Q  represents  the  heat  of  the  reaction  at  ordinary  temperatures; 

•Ber.,  1907,  40,  2,134. 

•  J.  Chem.  8oc.t  1912,  101,  91. 


HYDROGEN  FROM  HYDROCARBONS  149 

2n  =  the  algebraic  summation  of  the  number  of  mols  of  gaseous 
participants  in  the  reaction,  reactants  counted  positive  re- 
sultants negative.  In  this  case  2n  =  1  — 1  =  0;  hence  the 
2nd  term  falls  away. 

2nC  =  the  algebraic  summation  of  the  chemical  constants  of  the 
reacting  gases,  multiplied  in  each  case  by  the  number  of 
molecules  taking  part  in  the  reaction.  In  this  case  Cg 

=  1.6;     Cc  H  =  3.2.       Hence     2nC  =  1  X  3.2  —  i  X  1.6 

=  i.e.4 

The  equation  therefore  becomes: 

P(C2H2)  1  — x  40,000 

log  K  =  log  =  log  = f- 1.6. 

PH2  x  4'57T 

From  this  equation  the  following  values  result  for  (1  —  x),  the 
amount  of  undecomposed  acetylene  in  equilibrium  with  hydrogen 
and  carbon  at  the  given  absolute  temperatures 

T=  300°  1,000°  2,000°  3,000° 

1  — x  10-26  10-5  0.16  4.8 

It  will  be  seen  that  over  all  the  ordinary  temperature  range 
acetylene  may  be  practically  quantitatively  decomposed.  Only 
at  temperatures  attainable  by  the  electric  arc  is  acetylene  stable 
in  marked  quantity. 

In  a  similar  manner  it  can  be  established  that,  of  the  satur- 
ated paraffins,  methane,  ethane,  propane,  the  former  is  the  most 
stable  within  the  temperature  range  below  1,000°  C.  although  it 
'has  the  smallest  heat  of  formation.  This  would  suggest  that 
carbon  and  hydrogen  could  be  more  easily  prepared  by  thermal 
decomposition  of  the  more  complex  paraffins  than  from  methane. 
It  must  be  observed,  however,  that  the  thermal  degradation  proc- 
ess is  not  the  simple  process  indicated  by  the  equilibrium  equation 

CxH2y  =  xC  +  yH2 

4  Tables  of  values  for  the  chemical  constants  of  different  common  gases 
are  to  be  found  in  Lewis,  "System  of  Physical  Chemistry,"  Vol.  II,  p.  75,  1919 
Edition.  For  calculations  involved  in  the  study  of  hydrogen  production  the 
following  comprise  a  useful  selection  of  such  constants: — H,=  1.6;  CH4=2.8; 
Oa  =  2.8  ;  CO  =  3.5  ;  H2S  =  3.0  ;  SO2  =  3.3  ;  CO2  =  3.2  ;  CS2  =  3.1 ;  HaO  =  3.6  ; 
C2H2  =  3.2.  When  an  actual  value  for  C  is  not  available  it  is  evident  from 
the  majority  of  the  examples  cited  that  the  value  3.0  can  be  used  as  a  first 
approximation  for  the  unknown  chemical  constants. 


150  INDUSTRIAL  HYDROGEN 

but  that  the  decomposition  proceeds  in  stages.  As  methane  is 
undoubtedly  one  of  these  stages,  the  more  complex  paraffins 
should  require  as  high  a  temperature  as  methane  for  complete 
decomposition.  Furthermore,  it  must  be  borne  in  mind  that 
methane  is  an  extremely  stable  hydrocarbon,  the  velocity  of 
decomposition  being  abnormally  slow  until  temperatures  in  the 
neighbourhood  of  1,000°  C.  are  reached.  Even  with  catalytic 
agents,  at  this  temperature,  decomposition  is  not  particularly 
rapid. 

Alternative  to  processes  of  thermal  decomposition  the  produc- 
tion of  hydrogen  by  interaction  of  hydrocarbons  with  steam  has 
also  been  attempted.  The  procedure  may  be  explained  by  refer- 
ence to  the  case  of  methane.  Interaction  of  methane  and  steam 
yields  a  mixture  of  hydrogen  and  oxides  of  carbon  as  represented 
in  the  equations 

H20  =  CO  +3H2 
2H20  =  C02  +4H2 

These  reactions  are  reversible,  the  reverse,  or  methane  forming, 
reaction  being  utilised  in  other  circumstances  (see  Chapter  X) 
for  the  removal  of  carbon  monoxide  and  carbon  dioxide  from  hy- 
drogen. The  process  is  one  of  catalytic  hydrogenation  in  the  pres- 
ence of  reduced  nickel  or  other  suitable  catalyst  at  temperatures 
within  the  range  of  200-400°  C.  At  higher  temperatures  and 
especially  in  the  presence  of  excess  of  steam,  the  reaction  proceeds 
in  the  direction  of  hydrocarbon  decomposition.  The  equilibria 
prevailing  in  these  two  reactions  are  calculable  from  thermal 
data  by  nieans  of  the  Nernst  approximation  formula.  In  the 
reaction: 

CO  +  3H2  =  CH4  +  H20  +  Q  calories, 
Q  =  -26,300  +  18,400  +  57,600  =  49,700  cals. 

2n=l  +  3-l-l  =  2 
2nC  =  3.5  +  3  (1.6)  -  2.8  -  3.6  =  1.9 
Hence 

PCO  x  P(H2) 2          49,700 
logKp  =  log-   — —     -=-__  + 3.5  log  T  + 1.9, 

PCH,  x  PH2o        4-571 1 

the  partial  pressures  of  the  several  gases  being  expressed  in  at- 
mospheres. From  the  equation,  the  following  values  for  Kp  at 
different  temperatures  have  been  calculated 


HYDROGEN  FROM  HYDROCARBONS  151 

T°    Abs.  =  500  800  1,000  1,500 

Kp=  4X10-11    0.03  35  6X105 

In  a  similar  manner  it  can  be  shown  for  the  reaction 

C02  +  4H2  =  CH4  +  2H20 
that 

PC02  X  PH^  4.571  T 

logkp  =  log-    —  ^-       '-=-——  +3.51ogT-0.4 

PCH4XP(H20)  39>301 

whence  the  following  values  are  calculable: 

T°    Abs.  =  500  800  1,000  1,500 

Kp  =  7X10-9       0.1  31.7  105 

Both  reactions  therefore  share  a  common  feature.  The  equi- 
librium position  is  in  each  case  very  sensitive  to  temperature. 
Below  500°  Abs.  the  equilibrium  is  in  each  case  practically  quan- 
titatively on  the  methane  side.  Above  this  temperature  the 
equilibrium  position  tends  more  and  more  to  the  side  of  carbon 
monoxide  or  carbon  dioxide  and  hydrogen.  A  knowledge  of  these 
equilibria  demonstrate  why  the  methanation  process  is  to  be 
conducted  in  the  temperature  region  of  200°  -300°  C.  and  why, 
for  the  interaction  of  methane  and  water  to  yield  hydrogen,  high 
reaction  temperatures  are  essential. 

One  further  possibility  in  the  production  of  hydrogen  from 
hydrocarbons  may  here  be  mentioned  although  so  far  as  is  known 
it  has  not  been  attempted  technically.  Under  the  influence  of 
high  temperatures  methane  should  react  with  carbon  dioxide  to 
yield  hydrogen  and  carbon  monoxide  according  to  the  equation 

CH4  +  C02  =  2CO  +  2H2 

The  equilibrium  in  this  reaction  is  also  of  the  same  nature  as 
those  immediately  preceding.  Application  of  the  Nernst  approx- 
imation formula  gives: 

2CO  +  2H2  =  CH4  +  C02  +  60,100  cals. 
Hence 


PCO        P  60,100 

logKp  =  log  --  —  -1    = 

PCH4XPC02 


152  INDUSTRIAL  HYDROGEN 

which  equation  gives  the  following  calculated  values  for  Kp  at 
different  absolute  temperatures: 

T°    Abs.  =  500  800  1,000  1,500 

Kp=  2X10-13    0.008  0.4  3.5  X109 

It  will  be  seen  that,  in  this  case  also,  the  gradient  of  the 
equilibrium  with  temperature  is  steep.  Also,  it  may  be  noted 
that  a  somewhat  higher  temperature  would  be  necessary  in  this 
case,  in  order  that  the  methane  decomposition  with  carbon  diox- 
ide be  carried  to  the  same  degree  of  completeness  as  is  attainable 
using  steam. 

In  reference  to  all  three  reactions  it  must  be  observed  that, 
once  the  hydrocarbon  is  decomposed  and  hydrogen  and  carbon 
oxides  produced,  these  reaction  products  interact  among  them- 
selves in  a  manner  dependent  on  the  water-gas  equilibrium 

CO  +  H20  =  C02  +  H2 

which  at  any  given  temperature  will  determine  the  relative 
amounts  of  these  substances  present  in  equilibrium.  (See  Chap- 
ter III.) 

Processes  of  Thermal  Decomposition. —  (a)  From  coal-gas. 
Proposals  to  make  hydrogen  from  coal-gas  are  to  be  found  quite 
early  in  the  literature  of  hydrogen  production.  Thus,  St.  John 
(B.  P.  1,466/1876)  claimed  the  decomposition  of  the  hydro- 
carbons in  coal-gas  by  passage  of  the  gas  through  a  body  of  in- 
candescent coke.  The  need  for  hydrogen  was  at  that  time  small 
and  the  translation  of  the  proposal  into  actual  practice  was  not 
realised  until  much  later.  Many  patents  have  subsequently  been 
obtained  on  special  methods  of  conducting  the  process.  Lessing 5 
proposed  a  definite  temperature  interval  of  1,000-1,300°  C. 
and  retorts  either  empty  or  filled  with  carbon  as  a  vehicle  for 
the  attainment  of  the  necessary  temperature.  Since  the  thermal 
decomposition  of  hydrocarbons  does  not  remove  carbon  monox- 
ide, the  patent  of  Nauss  (B.  P.  2,298/1910)  proposed  the  removal 
of  this  constituent  by  passage  of  the  coal-gas  over  reduced  nickel 
at  200-300°  C.  whereby  transformation  to  methane  occurs  at  the 
expense  of  the  hydrogen 

CO  +  3H2  =  CH4  +  H20. 

•B.  P.  15,071/1909. 


HYDROGEN  FROM  HYDROCARBONS  153 

It  may  be  pointed  out  that  any  carbon  dioxide  could  be  removed 
by  the  same  treatment.  The  operation  however  would  be  beset, 
technically,  with  considerable  difficulty  unless  means  were  first 
devised  for  removal  of  the  carbon-sulphur  compounds  in  the 
coal  gas.  These  would  poison  the  nickel  catalyst  and  destroy  its 
efficiency  as  a  methanating  agent.  The  gas  after  hydrogenation 
of  the  oxides  of  carbon  was  next  to  be  subjected  to  a  tempera- 
ture of  1,000°-1,200°  C.,  in  which  stage  thermal  decomposition  of 
the  hydrocarbons  to  yield  carbon  and  hydrogen  would  be 
achieved. 

The  two  processes  which  have  come  into  technical  application 
for  hydrogen  production  from  coal-gas,  namely,  the  Oechelhauser 
and  the  Bamag-Bunte  processes,  do  not  involve  such  an  elabo- 
rate procedure.  As  a  result  the  product  in  each  case  represents 
only  a  crude  form  of  hydrogen. 

The  Oechelhauser  process  consists  in  passing  coal-gas  through 
coke  which  has  been  preheated  to  1,200°  C.  The  coke  acts  par- 
tially as  a  filtering  medium  partially  freeing  the  gas  produced 
from  the  carbon  formed.  The  residual  carbon  is  removed  by  fil- 
tration of  the  gas  through  wood  shavings.  It  is  claimed  that, 
in  this  manner,  a  total  elimination  of  the  heavier  hydrocarbons 
could  be  secured  and  a  reduction  of  the  methane  content  from 
about  25  to  less  than  7  per  cent.  The  carbon  monoxide,  normally 
present  in  coal-gas  to  the  extent  of  7  per  cent  is  not  appreciably 
altered  in  the  process.  As  ordinary  coal-gas  contains  nitrogen 
to  the  extent  of  several  per  cent  this  gas  would  also  be  a  fur- 
ther impurity.  The  product  therefore  would  be  a  hydrogen  of 
doubtful  applicability  for  the  usual  uses  to  which  hydrogen  is 
put.  Its  cost  per  unit  volume  should  not  be  greater  than  that  of 
the  original  coal-gas  since  the  expense  of  the  operation  should  be 
compensated  for  by  the  increase  in  gas  volume  accompanying 
the  methane  decomposition. 

The  Bamag-Bunte  Process  is  similar  in  essentials  and  differs 
in  detail.  The  coal-gas  is  freed  from  carbon  dioxide  before 
passage  over  white-hot  coke.  A  purification  from  carbon  monox- 
ide by  passage  over  heated  soda-lime  (see  Chapter  X)  is  also 
proposed.  Nitrogen  would  then  be  the  remaining  residual,  which, 
unless  special  precautions  were  taken  with  the  original  coal-gas 
production,  would,  however,  be  sufficiently  great  to  detract  con- 
siderably from  the  value  of  the  hydrogen  yield.  The  process  does 


154  INDUSTRIAL  HYDROGEN 

not  appear  to  possess  any  advantages  over  those  previously  dis- 
cussed involving  the  interaction  of  water-gas  and  steam.  The 
product  should  be  markedly  less  pure  with  an  operational  pro- 
cedure no  simpler  in  actual  practice. 

(b)  From  natural  gas,  petroleum  and  tar  oils. — Hydrogen 
from  petroleum,  natural  gas  and  tars,  is  produced  in  a  manner 
similar  to  that  described  in  the  last  section  and  several  technical 
applications  of  the  method  are  in  use  for  different  purposes. 

The  Rincker  and  Wolter 6  process  utilises  heavy  oils  or  tars 
for  the  production  of  hydrogen.  Two  generators  filled  with  coke 
are  used  for  the  decomposition  of  the  hydrocarbons.  The  coke 
is  brought  to  a  sufficiently  high  temperature  by  means  of  an  air 
blast,  the  air  producer  gas  from  the  first  generator  being  mixed 
with  a  supply  of  secondary  air  and  burnt  in  the  second  gener- 
ator. By  alternation  of  use  as  primary  and  secondary  gener- 
ators, both  bodies  of  coke  may  be  maintained  at  approximately 
equal  temperatures.  The  temperature  maintained  is  governed 
by  the  nature  of  the  oil  and  the  purity  of  the  product  desired, 
as  would  be  anticipated  from  the  theoretical  considerations  ad- 
vanced in  the  introductory  discussion  to  this  chapter.  For  hy- 
drogen production,  the  operating  temperature  is  in  the  neigh- 
bourhood of  1,300°  C.  After  the  coke  has  been  heated  by  this 
air  blast,  oil  or  tar  is  rapidly  sprayed  on  to  the  coke  from 
sprayers  in  the  upper  portion  of  the  generators.  To  prevent 
thermal  decompsition  of  the  oil  or  tar  in  the  sprayers,  the  oil 
is  removed  immediately  after  delivery  of  the  charge,  by  blowing 
steam  through  the  sprayers.  In  contact  with  the  incandescent 
coke  the  oil  is  gradually  vaporised  and  decomposed,  the  gas 
formed  forcing  its  own  passage  to  the  purification  system  through 
water  seals.  The  air-blow  averages  1  minute,  while  the  decompo- 
sition period  is  about  20  minutes  in  duration. 

The  carbon  produced  by  the  decomposition  process  remains 
in  part  on  the  coke  and  is  consumed  in  the  subsequent  air-blow. 

The  gas  purity  attainable  is  said  to  be  in  the  neighbourhood  of 
96  per  cent  hydrogen,  the  residue  consisting  of  one-third  nitro- 
gen and  two  thirds  carbon  monoxide.  Undecomposed  hydrocar- 
bons, especially  methane,  are  doubtless  also  present.  The  im- 
purities represent  the  gas  present  in  the  generators  when  the  oil 
spray  is  started,  and  the  products  of  materials  other  than  hydro- 

•  F.  P.  391,867  and  391,868/1908. 


HYDROGEN  FROM  HYDROCARBONS  155 

carbons  in  the  oil.  A  purging  with  steam  might  bring  about  a 
diminution  of  the  nitrogen  content  but  not  of  the  carbon  mon- 
oxide. For  the  removal  of  this  latter  constituent  the  soda-lime 
treatment  has  also  been  proposed,  a  reduction  of  this  gas  to  less 
than  0.5  per  cent  being  claimed.  To  avoid  clinkering  troubles, 
Ellis  has  suggested 7  the  addition  of  a  small  proportion  of  lime  to 
the  charge  of  coke,  so  as  to  act  as  a  flux  for  the  ash  produced. 

As  a  portable  hydrogen-producing  plant,  the  Rincker  and 
Wolter  system  has  been  used  by  both  the  German  and  the  Russian 
Air  Services.  A  unit  capable  of  producing  3,500  cubic  feet  per 
hour  can  be  mounted  on  two  railway  trucks.  The  essentials  of 
the  plant  are  two  generators,  a  turbo-blower  for  the  air-supply 
and  an  oil  pump.  The  only  raw  materials  requiring  transport 
are  coke  and  oil.  The  hydrogen  produced  has  been  found  to  be 
sufficiently  pure  for  use,  without  additional  purification,  in  kite 
balloons. 

A  patent  to  Ellis 8  describes  an  apparatus  in  which  such  an 
operation  as  the  Rincker-Wolter  process  may  also  be  carried  out. 
A  checker-brickwork  chamber  is  substituted  for  the  second  coke 
generator.  Frank 9  employs  two  generators  containing  coke  or  a 
refractory  together  with  specially  purified  natural  gas  for  the 
same  purpose.  Barth  10  and  Lowe  1X  have  similar  proposals  for 
the  production  of  carbon  and  hydrogen.  Modifications  of  the 
Rincker-Wolter  process  studied  in  this  country  recently  have 
demonstrated  the  possibility  of  obtaining  a  96-98%  hydrogen  by 
this  process.  The  residual  gas  is  mainly  methane  and  carbon 
monoxide  which  arises  from  the  water  or  oxygen  compounds  pres- 
ent in  the  oil  or  introduced  during  the  operating  process. 

A  process  devised  by  Brownlee  and  Uhlinger  (U.  S.  P.  1,168,- 
931/1916;  1,265,043/1918)  has  been  utilised  to  produce  a  hydro- 
gen, suitable  for  cutting  and  welding  purposes,  from  natural  gas 
as  raw  material.  Petroleum  oils  may  be  substituted  for  natural 
gas  but  the  plant  is  not  then  so  simply  operated.  The  process 
differs  from  the  Rincker  and  Wolter  process  in  that  the  necessary 
heat  for  thermal  decomposition  is  obtained  by  combustion  of  a 
portion  of  the  natural  gas  with  air.  A  body  of  refractory  ma- 

7U.  S.  P.  1,092,903/1914. 
•U.  S.  P.  1,092,903/1914. 
•U.  S.  P.  1,107,926/1914. 
10  U.  S.  P.  1,729,925/1916. 
"U.  S.  P.  1,174,511/1916. 


156  INDUSTRIAL  HYDROGEN 

terial  is  substituted  for  coke  as  the  vehicle  of  heat  storage.  Spe- 
cial attention  is  paid  to  ensuring  the  absence  of  easily  reducible 
oxides  in  the  refractory.  The  operating  temperature  is  above 
1,200°  C.  Pressures  greater  than  atmospheric  are  preferred.  In 
the  main,  the  carbon  formed  in  the  decomposition  reaction  is  car- 
ried along  with  the  hydrogen  and  may  be  removed  from  the  gas 
by  water  washing.  Any  carbon  remaining  in  the  refractory  sys- 
tem is  burned  away  in  the  subsequent  air-blow.  The  carbon 
produced  is  suitable  for  certain  purposes  to  which  lamp-black  is 
put,  though  it  is  of  inferior  quality  to  the  product  obtained  by 
incomplete  combustion  of  natural  gas. 

Operated  for  a  cutting  or  welding  product  a  gas  containing 
90-93  per  cent  hydrogen  is  produced,  the  residue  consisting 
mainly  of  carbon  monoxide  and  nitrogen  with  a  little  unchanged 
methane.  For  purposes  in  which  a  purer  hydrogen  is  required, 
it  is  claimed  that  the  initial  product  may  be  obtained  with  a 
hydrogen  content  greater  than  95  per  cent.  This  presupposes, 
however,  a  fairly  pure  natural  gas.  Natural  gas  with  a  high  con- 
tent of  inerts  would  obviously  be  useless  for  pure  hydrogen  pro- 
duction. The  economy  of  hydrogen  production  by  this  process 
compares  favorably  with  that  of  other  processes  when  a  high 
purity  is  not  essential.  The  addition  of  a  purification  system, 
however,  would  materially  enhance  the  cost  of  the  process.  Spe- 
cial consideration  will  be  given  to  such  processes  at  a  later 
stage. 

The  deterioration  in  the  quality  of  carbon  black  produced  by 
processes  of  thermal  decomposition  is  ascribed  by  Bacon,  Brooks 
and  Clark  to  the  length  of  time  which  the  carbon  remains  in  the 
heated  zone  of  the  system.  The  rich  lustrous  black  which  is 
first  produced  changes  to  a  dull  grey  product  when  kept  at  a 
temperature  of  1,200°  C.  To  ensure  a  rapid  removal  of  carbon 
from  the  heated  zone  with  the  consequent  recovery  of  both  car- 
bon and  hydrogen  in  a  form  of  maximum  commercial  value,  is  the 
object  of  the  patent  proposals  of  Bacon,  Brooks  and  Clark.12 
The  liquid  hydrocarbon  is  supplied  in  a  thin  stream  to  the  de- 
composition zone  of  the  plant  which  is  made  up  of  the  annular 
walls  of  a  series  of  graphite  rings  which  are  heated  to  a  tempera- 
ture exceeding  1,200°  C.  by  means  of  an  electric  current,  and 
are  encased  in  a  gas-tight  refractory  lining  having  an  outside 

»U.  S.  P.  1,220,391/1917. 


HYDROGEN  FROM  HYDROCARBONS  157 

metal  shell.  By  adjustment  of  hydrocarbon  supply  and  decompo- 
sition temperature  a  sufficient  velocity  of  gas  flow  is  maintained 
through  the  decomposition  zone  so  that  the  carbon  black  is  held 
in  suspension  and  is  rapidly  carried  away  to  a  settling  chamber, 
the  hydrogen  formed  passing  thence  to  a  gas  holder. 

(c)  From  Acetylene. — The  decomposition  of  acetylene  has 
been  operated  by  the  Carbonium  Gesellschaft  of  Friedrichshafen 
for  the  production  of  carbon  black  with  hydrogen  as  a  by- 
product. Early  obstacles  to  the  successful  use  of  the  process 
consisted  in  the  low  grade  of  carbon  produced  and  difficulties  in 
technical  operation.  These  latter  were  overcome  by  operating 
according  to  the  patents  of  Machtolf,13  the  acetylene  being  sub- 
jected to  pressure  not  exceeding  6  atmospheres.  The  specifica- 
tions provide  one  chamber  for  explosion  of  the  gas  and  a  carbon- 
black  separator  into  which  the  gas-carbon  mixture  is  blown  and 
separated.  A  rotary  scraper  operating  within  the  explosion 
chamber  removes  lamp-black  adhering  to  the  walls  of  the  vessel 
and  prevents  its  accumulation  in  the  explosion  system.  When 
the  technical  difficulties  were  overcome  the  process  was  operated 
for  a  period  of  two  years,  the  by-product  hydrogen  being  used  by 
the  neighbouring  Zeppelin  station.  It  was  found,  however,  .that 
the  carbon  black  produced  was  inferior  to  the  better  grades  of 
American  carbon  black  and  consequently  could  not  command  an 
equal  price  in  the  market.  This  rendered  the  process  uneconom- 
ical and  according  to  information  available  in  1914  the  process 
had  been  discontinued.  It  is  not  known  whether,  in  recent  years, 
the  plant  has  again  come  into  use. 

The  thermal  decomposition  of  acetylene  has  been  proposed 
by  Pictet.14  Since  the  formation  of  acetylene  from  its  elements 
is  an  endothermic  reaction,  the  decomposition  is  accompanied  by 
the  evolution  of  heat.  Consequently  a  tube  heated  initially  to 
500°  C.  would  rapidly  rise  in  temperature  when  acetylene  was 
decomposed  within  the  tube,  unless  special  devices  were  installed 
to  keep  the  temperature  constant.  Pictet  suggested  a  variety  of 
ways  in  which  this  could  be  accomplished.  The  heat  of  reaction 
is  more  than  sufficient  to  keep  the  process  thermally  self-sus- 
taining. Hence,  after  the  reaction  has  started,  external  heat  is 
unnecessary,  the  incoming  gases  being  automatically  raised  to 

18  D.  R.  P.  194,301/1905  ;  194,939/1905  ;  207,520/1907.     B.  P.  14,601/1906. 
14  B.  P.  24,256/1910;  F.  P.  421,838/1910. 


158  INDUSTRIAL  HYDROGEN 

reaction  temperature.  The  outlet  end  of  the  reaction  tube  can 
be  cooled  to  prevent  deterioration  of  the  carbon-black  resulting 
from  the  decomposition.  The  surplus  heat  may  also  be  used  up 
in  the  evaporation  and  thermal  decomposition  of  liquid  hydro- 
carbons having  a  positive  heat  of  formation.  Various  other  pro- 
posals involving  the  use  of  steam  and  the  production  of  a 
hydrogen-carbon  dioxide  mixture  are  also  included  in  the  patent 
specifications.  It  seems  unlikely  that  any  of  these  proposals  can 
have  reached  a  technical  stage  of  development  partly  owing  to 
the  raw  materials  cost  and  partly  owing  to  the  difficulties  which 
the  technical  control  of  such  mixed  reactions  would  involve. 

Processes  of  Interaction  with  Steam. — To  promote  the  de- 
composition of  hydrocarbons  at  lower  temperatures  than  is  pos- 
sible with  exothermic  hydrocarbons  by  processes  of  purely  ther- 
mal decomposition,  interaction  with  steam  in  presence  of  a  cata- 
lyst has  been  the  object  of  many  patent  claims.    As  long  ago 
as  1880  Stern 15  suggested  the  use  of  lime  as  contact  agent  for 
the  decomposition  of  naphtha  by  steam.    Dieffenbach  and  Mol- 
denhaur 16  claim  as  active  catalytic  agents  wire  gauze  made  of 
nickel,  cobalt,  platinum  or  similar  metals.     By  disposing  the 
gauze  at  right  angles  to  the  direction  of  gas  flow,  a  very  short 
time  of  contact  and  thereby  a  sudden  cooling  of  the  reaction 
products  could  be  secured.    Operating  in  this  manner,  it  was  sug- 
gested that  the  carbon  dioxide  formed  has  little  opportunity  to 
be  reduced  to 'carbon  monoxide.    Oxygen  could  be  added  if  de- 
sired to  maintain  reaction  temperatures.    It  is  extremely  doubt- 
ful whether  this  process  could  be  operated  to  yield  a  hydrogen- 
carbon  dioxide  mixture.    Subsequent  reaction  at  a  lower  tempera- 
ture to  cause  the  interaction  of  steam  with  any  carbon  monoxide 
produced  to  yield  carbon  dioxide  and  hydrogen  would,  therefore, 
seem  to  be  necessary.    The  patent  to  the  Badische  Co.17  specifies 
the  use,  as  catalyst  for  the  same  reaction,  of  a  refractory  oxide 
such  as  magnesia,  acting  as  catalyst  support  to  nickel  present  in 
the  refractory  in  concentrations  ranging  from  2  to  5  per  cent  and 
maintained  at  a  temperature  of  8000-1,000°  C.    Any  carbon  mon- 
oxide formed  was  to  be  removed  in  a  subsequent  operation.  Ex- 

15  B.   P.   2,787/1880. 

18  D.   R.   P.   229,406/1909. 

"B.  P.  12,978/1913. 


HYDROGEN  FROM  HYDROCARBONS  159 

periments  with  this  process  using  such  a  catalyst  and  hydrogen 
containing  small  concentrations  of  methane  gave  poor  results. 
This  suggests  that,  even  at  the  high  temperatures  specified,  the 
hydrogen-carbon  monoxide  mixture  produced  by  interaction  of 
steam  and  hydrocarbons  would  contain  residual  undecomposed 
hydrocarbons  unless  impracticably  low  velocities  of  reaction  were 
employed. 

Pictet18  suggests  the  use  of  high  temperatures  alone  for  the 
production  of  hydrogen  and  carbon  monoxide  from  petroleum 
and  steam. 

In  the  preparation  of  a  nitrogen-hydrogen  mixture  suitable 
for  ammonia  synthesis  it  has  been  stated  that  the  use  of  an  air- 
steam-producer  gas-water-gas  mixture  results  in  a  hydrogen- 
carbon  dioxide-steam  mixture  containing  only  the  equilibrium 
concentration  of  methane  (see  page  75)  when  an  iron  oxide 
catalyst  at  500°-600°  C.  is  used.  The  writer  has  not,  thus  far, 
been  able  to  confirm  this  result  experimentally.  The  point  how- 
ever is  one  of  considerable  technical  importance  since  it  sug- 
gests the  possible  utilisation  of  cheap  gaseous  by-products  such 
as  coke-oven  gas  for  the  production  of  hydrogen-nitrogen  mix- 
tures for  ammonia  synthesis. 

"B.  P.  14,703/1911. 


Chapter  IX. 
Miscellaneous  and  By-Product  Hydrogen  Processes. 

The  Decomposition  of  Alkali  Formates. — Alkali  formates 
when  subjected  to  moderate  heat  yield  the  corresponding  oxalate 
with  evolution  of  hydrogen 

2HCOONa  =  (COONa)2  +  H2. 

Since  the  development  of  synthetic  methods  for  the  production 
of  formates  this  reaction  has  become  increasingly  important  and 
capable  of  yielding  marked  amounts  of  hydrogen  gas  as  a  by- 
product. Thus,  in  the  production  of  a  2,000  Ib.-ton  of  oxalic 
acid,  the  by-product  hydrogen  should  amount  to  not  less  than 
8,000  cubic  feet. 

The  reaction  is  ordinarily  conducted  with  the  sodium  salt. 
Sodium  formate  can  be  prepared  in  a  variety  of  ways,  from 
caustic  soda  as  starting  point,  utilising  one  or  other  of  the  tech- 
nical fuel  gases  as  source  of  carbon  monoxide. 

Formate  Synthesis—  Goldschmidt's  patent  (B.  P.  17,066/ 
1895)  claims  the  production  of  formate  by  the  action  of  com- 
pressed carbon  monoxide  on  caustic  soda  or,  preferably,  soda- 
lime,  at  a  temperature  of  230°  C.  The  Elektrochemische  Werke, 
Bitterfeld,1  use  a  much  lower  reaction  temperature  of  100°-120°  C. 
employing  the  gas  under  pressure.  The  presence  of  small  quan- 
tities of  moisture,  0.1  to  0.15  per  cent  water,  in  the  caustic 
soda,  accelerates  absorption  according  to  the  claims  of  Nitrid- 
fabrik  G.  m.  b.  H.2  The  use  of  caustic  soda  solutions  as  absorp- 
tion medium  is  the  claim  of  other  manufacturers.  Koepp  and 
Co.3  use  a  35  per  cent  solution  and  a  temperature  of  220°  C., 
requiring,  therefore,  the  employment  of  pressure.  A  later  patent 4 
replaces  the  alkali  solution  by  alkali  salts  in  admixture  with 

1  B.  P.  772/1906. 

2  B.  P.  9,008/1906. 
8  B.  P.  7,875/1904. 

<D.  B.  P.  212,641/1904. 

160 


BY-PRODUCT  HYDROGEN  PROCESSES  161 

alkaline-earth  hydroxides  or  by  alkaline-earth  hydroxides  alone. 
Weise  and  Rieche  5  specify  a  20  per  cent  soda  liquor  heated  with 
the  gas  containing  carbon  monoxide  under  pressure.  The  United 
Alkali  Co.6  claim  that  rapid  and  complete  absorption  is  ob- 
tained with  the  solid  absorbent  if  titanic  acid  to  the  extent  of 
11  per  cent  is  present  in  the  reaction  mass.  Norris7  claims  the 
use  of  ferric  oxide  for  the  same  purpose. 

Meister  Lucius  and  Briining8  employ  a  calcined  alkali  car- 
bonate and  desiccated  calcium  hydroxide  as  the  absorption  agent. 
Ellis  and  McElroy 9  employ  calcium  carbonate  suspended  in 
water  as  the  absorption  agent,  using  carbon  monoxide  or  air  pro- 
ducer gas  under  pressure  to  effect  the  conversion  to  formate. 
Dubosc,  Luttringer  and  Denis 10  propose  the  use  of  ammonia  or 
organic  bases  in  presence  of  metallic  catalysts  at  temperatures 
between  90°  and  170°  C.  at  atmospheric  pressure.  Katz  and 
Ovitz  (U.  S.  P.  1,212,359/1917)  allow  a  32  per  cent  solution  of 
sodium  hydroxide  to  pass  downwards  in  a  finely  divided  con- 
dition through  a  tower  up  which  a  stream  of  ammonia  and  car- 
bon monoxide  is  passing.  A  pressure  of  10-20  atmospheres  and 
temperatures  been  150°  and  220°  C.  are  specified.  Lackmann's 
patent J1  is  similar  to  the  earliest  patents  and  uses  granular  so- 
dium hydrate  passing  counter  current  to  a  stream  of  preheated 
water-gas  or  other  gas  rich  in  carbon  monoxide. 

Formate  Decomposition. — As  already  stated,  the  decompo- 
sition of  sodium  formate  is  ordinarily  undertaken  with  a  view 
to  maximum  oxalate  yield.  The  precautions  taken  in  this  di- 
rection, however,  also  favour  pure  hydrogen  production,  since  the 
impurities  in  the  gas  arise  from  oxalate  decomposition.  A  sum- 
mary of  a  study  of  the  process  recently  made  by  Leslie  and 
Carpenter 12  shows  that  the  best  conditions  for  the  conversion  of 
sodium  formate  to  oxalate  are  the  following:  (1)  the  admixture 
of  sodium  hydroxide  approximating  one  per  cent  of  the  formate;13 

BU.  S.  P.  1,098,139/1914. 

«B.  P.  13,953/1907. 

7B.   P.   4,684/1910. 

«B.   P.   8,012/1908. 

»U.  S.  P.  875,055/1907. 

10  U.  S.  P.  1,019,230/1912. 

"  U.  S.  P.  1,274,169/1918. 

«  Chem.  &  Met.  Eng.,  1920,  22,  1,195. 

"  Cf.  Koepp  &  Co.,  B.  P.  9,327/1903. 


162  INDUSTRIAL  HYDROGEN 

(2)  an  absolute  pressure  approximating  14  inches  of  mercury;14 

(3)  a  temperature  of  350°  C.    As  it  is  a  matter  of  difficulty  to 
heat  a  large  quantity  of  formate  quickly  to  350°  C.  the  con- 
version processes  should  be  a  continuous  one  in  which  small  quan- 
tities of  formate  only  are  subjected  to  the  influence  of  the  ex- 
perimental conditions  at  any  one  time.    Unless  the  reaction  mass 
is  brought  quickly  to  the  stated  reaction  temperature  other  de- 
composition products  result  in  greater  or  less  degree.    With  these 
conditions  observed  a  90  per  cent  conversion  to  oxalate  can 
readily  be  secured. 

The  hydrogen  produced  will  contain  varying  quantities  of 
carbon  monoxide  dependent  on  the  efficiency  of  the  conversion 
process.  The  secondary  decomposition  of  sodium  oxalate  yields 
sodium  carbonate  and  carbon  monoxide. 

Na2C204  =  Na2C03  +  CO. 

It  is  apparent  that,  both  from  the  oxalate  and  the  hydrogen 
standpoint,  this  is  undesirable.  The  gas,  if  containing  undue 
amounts  of  carbon  monoxide,  would  require  purification  by  one 
or  other  of  the  methods  given  in  the  succeeding  chapter.  No 
data  as  to  purity  of  hydrogen  attainable  seem  to  be  available, 
as,  hitherto,  the  process  has  been  conducted  solely  for  oxalate 
production. 

It  should  be  pointed  out  that  the  decomposition  of  metallic 
formates  does  not  always  yield  the  corresponding  oxalate.  Dry 
distillation  of  calcium  formate  has  long  been  known  to  yield  for- 
maldehyde, methyl  alcohol,  some  acteone  and  also  empyreumatic 
products  in  addition  to  gaseous  products  containing  hydrogen, 
carbon  monoxide  and  carbon  dioxide.  Solutions  of  the  formates 
of  zinc,  lead,  tin,  copper,  nickel  and  cobalt  were  shown  by 
Ribau,15  who  heated  the  solutions  in  sealed  tubes  at  175°  C.,  to 
yield  hydrogen,  carbon  dioxide,  metallic  oxide  or  carbonate.  Ru- 
bidium, calcium,  barium  and  magnesium  formates  at  360°-420°  C. 
give  carbonate,  no  oxalate,  and  a  gas  containing  the  oxides  of 
carbon.16  Goldschmidt 17  showed  that  stannous  formate  gave 

"  Cf.  Elektrochemtsche  Werke  Bitterfeld.    B.  P.  19,943/1907. 
»  Compt.  rend.,  1881,  93,  1,023,  1,082. 
"Merz  and  Weith,  Bar.  1882,  15,  1,507. 
?TD.  R.  P.  183,856/1906. 


BY-PRODUCT  HYDROGEN  PROCESSES  1G3 

high  yields  of  formaldehyde  and  methyl  formate  when  heated. 

3(HCOO)2Sn  =  3Sn02  +  3HCHO 
2HCHO  =  HCOOCH3. 

The  hydrogen-yielding  reaction  is  entirely  secondary  in  this  case. 
The  problem  of  formate  decomposition  has  recently  been  studied 
in  detail  by  Hoffmann  and  his  co-workers  18  who  have  shown  that, 
with  most  formates,  products  other  than  hydrogen  and  the  cor- 
responding oxalate  result.  With  sodium  and  potassium  formates 
however,  hydrogen  is  the  first  volatile  product,  oxalate  being 
formed,  secondary  decomposition  then  leading  to  carbonate  and 
carbon  monoxide. 

Hydrogen  from  Dehydrogenation  Processes 

It  is  possible  that  the  development  which  has  occurred  in  the 
last  two  decades  in  regard  to  catalytic  hydrogenation  processes 
will  be  paralleled  in  the  coming  years  by  a  similar  development 
in  dehydrogenation  processes.  In  such  case,  hydrogen  will  be 
produced  in  quantity  whereas  now  it  is  consumed.  The  logical 
development  would  seem  therefore  to  be  an  extended  effort  to 
combine  in  one  plant  dehydrogenation  processes  with  processes 
of  hydrogenation  so  that  the  hydrogen  produced  in  one  operation 
could  be  utilised  in  the  other.  As  an  example  of  such  from  the 
history  of  the  past  few  years  the  case  of  Messrs.  Crosfield  of 
Warrington,  England,  may  be  cited.  Armstrong  and  Hilditch 
have  recently  recorded 19  that,  during  the  war  many  hundreds 
of  tons  of  alcohol  were  dehydrogenated  to  yield  acetaldehyde. 
The  hydrogen  by-product  was  utilised  for  the  hardening  of  liquid 
fats. 

It  is  outside  the  scope  of  this  volume  to  give  a  general  treat- 
ment of  the  problem  of  dehydrogenation.  Reference  may  be 
made  in  this  matter  to  recent  books  on  catalysis.20  The  general 
problem  may  be  illustrated,  however,  by  the  special  case  al- 
ready mentioned. 

Sabatier  and  Senderens  showed 2l  that  ethyl  alcohol,  when 

"Ber.,  1916,  49,  303;  1918,   51,  1,398. 
™  Proc.  Roy,  Soc.,  1920,  97A,  259. 

20  For  example :  Rideal  and  Taylor.  "Catalysis  in  Theory  and  Practice,"  pp. 
207-229.  Macmlllan  &  Co.,  1919. 

» Arm.  CMm.  PTvys.,  1905,   [8],  -J,  463. 


164 


INDUSTRIAL  HYDROGEN 


passed  over  heated  copper,  preferably  at  about  300°  C.,  is  re- 
solved into  acetaldehyde  and  hydrogen 

CH3CH2OH  =  CH3CHO  +  H2. 

This  process  was  developed  by  Messrs.  Joseph  Crosfield  and 
Sons,  Warrington,  England,  during  the  war,  into  a  technical  proc- 
ess whereby  the  aldehyde  was  produced,  in  large  scale  operation, 
with  a  conversion  efficiency  amounting  to  90-93  per  cent  calcu- 
lated on  the  alcohol  used.  From  20  to  25  per  cent  of  the  alcohol 
was  converted  at  each  passage  over  the  metal  into  an  equi- 
molecular  mixture  of  aldehyde  and  hydrogen.  To  obtain  the 
former,  the  vapors  were  cooled  and  then  passed  into  an  elaborate 
fractionating  column  in  which  the  aldehyde  was  separated  from 
the  hydrogen  and  alcohol. 

The  technical  operations  may  be  deduced  from  the  following 
tables  compiled  from  an  experimental  study  of  the  process  by 
Armstrong  and  Hilditch.  These  authors  state  that  the  propor- 
tion of  by-products  in  their  experiments  was  of  the  order  obtained 
in  the  actual  large  scale  process. 


Alcohol 
Per  Cent 

Tem- 
pera- 
ture 

Gas  Evolved 

Ratio 
CHZCHO:H2 

H2 

C02 

C2H4 

CO 

"CHS 

Anhydrous 
92 
92 
92 
75 
50 

300°  C. 
300 
330-335 
325-330 
325-330 
325-330 

76.6 
91.0 
97.1 
98.9 
98.0 
91.7 

2.4 
1.5 

0.7 
0.3 

3.5 
0.0 

8.7 
4.0 

.67 
.95 
.55 
.67 
.83 
.83 

It  is  evident  (a)  that  the  presence  of  water  improves  the 
yield  of  acetaldehyde  relative  to  that  of  hydrogen,  (b)  Using 
alcohol  of  a  given  concentration  (e.  g.,  92  per  cent),  as  the  tem- 
perature is  raised,  the  yield  of  aldehyde  is  considerably  lessened, 
although  the  amount  of  alcohol  decomposed  and  the  volume  of 
hydrogen  produced  are  much  increased.  At  330°  C.  the  pro- 
portion of  alcohol  attacked  is  about  50  per  cent  of  the  total 
quantity  passed  as  against  20-25  per  cent  at  300°  C.  (c)  At  the 
higher  temperature  the  yield  may  be  partially  restored  by  using 


BY-PRODUCT  HYDROGEN  PROCESSES          165 

alcohol  containing  a  larger  proportion  of  water,  (d)  Even  at 
300°  C.,  if  alcohol  rendered  as  anhydrous  as  possible  be  used, 
the  yield  falls  seriously,  (e)  The  use  of  92  per  cent  alcohol 
instead  of  anhydrous  alcohol  raises  the  purity  of  the  hydrogen 
obtained. 

Whatever  the  conditions,  small  quantities  of  by-products 
were  always  produced,  the  total  amount  being  normally  of  the 
order  of  1  or  2  per  cent  of  the  aldehyde  formed. 

Assuming  a  90  per  cent  theoretical  hydrogen  yield  it  may  be 
calculated  that  per  2,000  Ib.-ton  of  alcohol  dehydrogenated  a  yield 
of  upwards  of  15,000  cubic  feet  of  hydrogen  can  be  produced. 
It  is  evident  that,  by  suitable  combination  of  such  a  process 
with  an  allied  hydrogenation  process,  economies  are  possible. 
It  is,  doubtless,  in  the  fine  chemicals  industry,  that  this  and 
other  by-product  hydrogen  processes  will  find  their  utility. 

Hydrogen  from  Fermentation  Processes. 

The  fermentation  of  starch  by  means  of  the  "Fernbach"  or 
"Weizmann"  process,  yields,  as  main  reaction  products,  acetone 
and  butyl  alcohol.  Fernbach  showed  in  1910  that  by  fermenta- 
tion of  starch-containing  materials  with  a  particular  micro-or- 
ganism the  products  were  acetone  and  butyl  alcohol  in  the 
ratio  of  1  :  2.  The  shortage  of  acetone  during  the  war  led  to  a 
development  of  this  process  with  the  aid  of  a  bacillus  of  the 
long  rod  type  which  was  furnished  to  the  British  Government 
by  Dr.  C.  Weizmann  of  Manchester.  The  manufacture  of  ace- 
tone by  means  of  this  culture  was  carried  on  in  Britain,  Canada 
and  the  United  States,  in  the  latter  country  at  the  plants  of  the 
Commercial  Distillery  Co.,  and  of  the  Majestic  Distilling  Co., 
Terre  Haute,  Indiana.22  The  manufacture  of  acetone  by  the 
Weizmann  process  attained  the  greatest  success  at  the  factory 
of  British  Acetones,  Toronto,  Ltd.,  in  Canada,  where  an  output 
of  200  long  tons  a  month  was  eventually  reached. 

As  medium  for  the  process  a  mash  containing  from  5-10  per 
cent  of  grain,  usually  maize,  was  employed.  Fernbach's  process, 
started  at  Kings  Lynn,  had  previously  employed  potatoes  which 
were  at  that  time  the  cheapest  raw  material  in  England.  An 

"  For  further  historical  discussion  of  this  subject  see  Conference  on 
Recent  Developments  in  the  Fermentation  Industries,  J.  Soc.  Chem.  Ind.t  1919, 
38,  271  T. 


166 


INDUSTRIAL  HYDROGEN 


important  by-product  in  the  fermentation  process  is  the  evolved 
gas,  which,  throughout  a  whole  fermentation  period,  will  analyse 
50  per  cent  hydrogen  and  50  per  cent  carbon  dioxide.  In  quan- 
tity, an  average  of  5.5  cubic  feet  of  mixed  gas  at  27°  and  760  mm. 
can  be  obtained  per  pound  of  maize  fermented.  The  ratio  of 
hydrogen  to  carbon  dioxide  is  not  constant  throughout  the  proc- 
ess as  shown  by  the  following  table  due  to  Reilly  and  others.23 


Time 

Gas.C.ft/hr 

C02 

H2 

Air 

June  28/16 

4  pm. 

.... 

100 

7  pm. 

253 

11.5 

38.5 

50 

8  pm. 

834 

27.1 

57.9 

15 

9  pm. 

822 

40.3 

55.2 

4.5 

10  pm.     . 

660 

40.0 

59.0 

3.0 

11  pm. 

760 

50.3 

47.2 

2.5 

June  29/16 

9.30  am. 

1186 

62  , 

38 

From  the  time  of  the  last  observation  to  the  end  of  the  fermenta- 
tion period  the  percentage  of  carbon  dioxide  did  not  alter.  Reilly 
and  his  co-workers  state  that  the  high  percentage  of  hydrogen  in 
the  early  stages  is  probably  due  to  solution  of  carbon  dioxide 
in  the  mash.  This  view  is  disputed  by  Speakman  24  who  showed 
by  experiment  that  the  gas  produced  at  the  immediate  commence- 
ment is  pure  hydrogen  the  percentage  of  which  begins  to  fall  due 
to  production  of  carbon  dioxide  with  increasing  rapidity.  For 
the  mechanism  of  the  fermentation  process  he  makes  the  fol- 
lowing suggestions  as  to  the  sequence  of  changes: 

xH20  =  x(C6H1206) 

Glucose 

CHCOOH  +  [02] 


xC6H1005 

Starch 

C6H1206  =  C3H7COOH  3 

Butyric  Acid  Acetic  Acid 

C3H7COOH  +  [02]  =  2CH3COCH2COOH 


2H 


C0 
H20 
CHCOOH      2H2  =  C2H5OH  +  H20. 


CH3COCH2COOH  =  CH3COCH3 
C3H7COOH  +  2H2  =  C4H9OH 


»  Biochemical  J.,  1920,  14,  229. 
2*  J.  Biol.  Chem.,  1920,  -}3,  401. 


BY-PRODUCT  HYDROGEN  PROCESSES  167 

The  purification  of  such  hydrogen  for  utilisation  in  various 
ways  should  not  be  difficult.  The  pressure  water-washing  process 
previously  discussed  (p.  72)  would  undoubtedly  be  the  sim- 
plest method  of  converting  the  mixed  gas  into  a  sufficiently  pure 
hydrogen  for  technical  use. 

The  commercial  feasibility  of  the  acetone-butyl  alcohol  is 
conditioned  by  the  use  which  may  be  made  of  both  main  products 
and  of  the  by-products.  The  solid  residue  from  the  fermenta- 
tion process,  approximately  13  per  cent  of  the  total  maize  used, 
has  a  high  oil  and  albuminoid  content.  Its  dilution  in  the  vat 
liquors  is  an  obstacle  to  its  successful  utilisation,  the  concentra- 
tion of  solid  matter  being  1  cwt.,  in  1,500  gallons  of  liquor.  The 
gases  evolved  have  a  distinct  potential  value  which  must  be 
taken  into  consideration  in  a  discussion  of  the  possibilities  of  the 
process. 

Fermentation  processes  yielding  mainly  acetone  and  ethyl 
alcohol  with  hydrogen  as  a  by-product  have  also  been  the  sub- 
ject of  experimentation.25 

The  Hydrogenite  Process. 

Analogous  to  the  silicol  and  aluminium  processes  for  the  prep- 
aration of  hydrogen  this  process  uses  ferro-silicon  and  alkali 
but  at  high  temperatures  with  a  relatively  small  amount  of 
water.  It  is  due  to  Jaubert 26  and  was  developed  essentially  for 
use  in  the  field. 

The  exothermicity  of  the  oxidation  of  silicon  to  the  dioxide  is 
the  basis  of  the  process 

Si  +  02  =  Si02  +  180,000  calories. 

This  reaction  is  sufficiently  energetic  that,  once  initiated,  the 
action  is  sufficiently  intense  to  bring  about  the  withdrawal  of 
oxygen  from  solid  sodium  hydroxide. 

The  material  employed  for  field  use  consists  of  25  parts  of 
ferro-silicon,  containing  upwards  of  90  per  cent  silicon,  60  parts 
of  caustic  soda  and  20  parts  of  soda  lime.  •  It  is  produced  in 
compressed  blocks  of  an  intimate  mixture  of  these  ingredients, 
originally  in  a  finely  powdered  form.  So  produced,  it  is  kept  in 

"Northrup,  Ashe  and  Senior.  J.  Biol.  CTiem,.,  1919,  39,  1;  J.  Ind.  Eng. 
Chem.,  1919,  11,  723. 

*<Rev.  Gen.  Chim.,  lSt  341,  357. 


168  INDUSTRIAL  HYDROGEN 

air  tight  containers  until  used.  For  use,  the  heavy  lid  is  first 
loosened  and  allowed  to  rest  on  the  container  placed  centrally 
in  a  water- jacketed  generator.  Reaction  is  started  by  applying 
a  match  to  a  small  quantity  of  powder  through  a  small  hole  in 
the  lid.  The  reaction  is  propagated  throughout  the  mass  of  solid 
and  hydrogen  is  liberated  at  a  high  temperature  with  great  ra- 
pidity. The  heat  of  reaction  is  sufficient  to  generate  steam  in  the 
water  jacket  of  the  generator  and  this  steam  is  finally  admitted 
to  the  reaction  mass,  increasing  the  hydrogen  evolution  and  slak- 
ing the  reaction  mass.  The  net  effect  of  the  whole  process  is 
therefore,  as  in  the  silicol  process, 

Si  +  2NaOH  +  H20  =  Na2Si03  +  2H2. 

It  will  be  seen,  however,  that  the  water  required  in  this  case  is 
much  less  than  that  in  the  silicol  process,  in  which  a  solution  of 
caustic  soda  is  employed. 

The  process  is  protected  by  numerous  patents  of  which  B.  P. 
153/1911  covers  the  reaction  as  just  described.  The  French  army 
has  used  the  process  in  the  field.  Waggons  holding  6  generators 
and  a  central  cooler  and  washer  have  a  capacity  of  5,000  cubic 
feet  of  hydrogen  per  hour.  The  product  is  of  a  high  purity  sim- 
ilar to  that  obtained  in  the  silicol  process.  The  weight  of  ma- 
terials necessary  to  the  process  is  about  200  Ibs.  per  1,000  cubic 
feet  of  hydrogen  and,  therefore,  about  one  and  one  half  times  the 
weight  requiring  transportation  in  the  silicol  process,  providing 
water  is  available  for  the  latter  at  the  point  of  use.  Where  this 
does  not  hold,  the  hydrogenite  process  is  manifestly  advantageous. 
The  cost  of  gas  production  is  higher  even  than  in  the  silicol 
process  due  to  the  greater  proportion  of  alkali  consumed. 

An  older  process  similar  in  principle  to  the  "hydrogenite" 
process  is  based  on  the  affinity  of  zinc  for  oxygen.  Heated  soda 
lime  and  zinc  dust  yield  hydrogen 

Zn  +  (NaOH  — Ca(OH)2)  =  ZnO  +  CaO  +  NaOH  +  H2. 
Experimental  work  on  this  reaction  was  conducted  by  Schwarz  27 
and  its  applicability  in  the  field  has  been  tested  by  Majert  and 
Richter. 

»  Ber.  1886.  19,  441. 


BY-PRODUCT  HYDROGEN  PROCESSES  169 

Hydrogen  from  Sulphides. 

Barium  sulphide  is  oxidised  by  steam  to  barium  sulphate,  hy- 
drogen being  simultaneously  formed. 

BaS  +  4H20  =  BaS04  +  4H2. 

The  barium  sulphate  may  then  be  reduced  by  coal  or  producer 
gas  to  regenerate  the  sulphide.28  The  process  does  not  seem  to 
offer,  as  yet,  technical  interest  sufficient  to  have  earned  for  it 
close  study. 

Combination  of  this  reaction  with  an  oxygen-generating  proc- 
ess is  proposed  by  Teissier  and  Chaillaux  (F.  P.  447,688/1912) 
in  the  following  sequence  of  reactions: 

BaS04  +  4MnO  =  BaS  +  4Mn02 

4Mn02  =  4MnO  +  202 
BaS  +  4H20  =  BaS04  +  4H2. 

Iron  pyrites  treated  with  steam  generates  hydrogen,  hydrogen 
sulphide  and  sulphur  dioxide.29  Temperatures  between  750°  and 
1,000°  C.  are  necessary.  On  cooling,  the  interaction  of  hydrogen 
sulphide  and  sulphur  dioxide  yields  sulphur. 

2H2S  +  S02  =  3S  +  2H20. 

Residual  sulphur  dioxide  may  be  removed  by  water  washing, 
hydrogen  sulphide  by  the  usual  purification  methods  (see  p.  173) . 

Hydrogen  from  Acids. 

Early  aeronautical  needs  were  supplied  from  acids  and  scrap 
metals.  Normally  such  processes  are  too  expensive  in  raw  ma- 
terials but  are  convenient  occasionally,  in  the  field,  as  special 
apparatus  is  not  required.  The  British  manual  of  military  bal- 
looning issued  in  1896  described  a  plant  for  use  in  such  cases. 
Dilute  sulphuric  acid  (1  acid  :  4  water)  was  employed,  30  gallons 
of  such  acid  being  used  for  60  Ibs.  of  granulated  zinc.  The  gas 
was  generated  in  a  copper  retort.  The  gas  was  freed  from  acid 
spray  by  passage  through  a  layer  of  granulated  zinc  in  a  second 
copper  chamber  and  passed  thence  through  a  water  scrubber  to  a 
gas  holder. 

28  Lahousse  Fr.  pat.  361,866/1905. 

29  Hooton  B.  P.  18,007/1914. 


170  INDUSTRIAL  HYDROGEN 

More  recently,  proposals  to  utilise  acids  for  hydrogen  pro- 
duction have  involved  waste  acids  or,  alternatively,  methods 
whereby  the  products  of  reaction  could  be  utilised  for  other  pur- 
poses. Thus,  the  utilisation  of  hydrochloric  acid  from  the  salt- 
cake  process  has  been  proposed,  a  tower  packed  with  scrap  iron 
to  be  used  for  absorption  of  the  gas  by  water,  the  hydrogen  pro- 
duced by  interaction  of  the  acid  and  iron  to  be  collected  and  the 
ferrous  chloride  worked  up  for  other  purposes.  The  interaction 
of  zinc  and  dilute  sulphuric  acid,  giving  hydrogen  and  zinc  sul- 
phate has  been  suggested,  provision  being  made  to  evaluate  the 
process  by  working  up  the  salt  for  the  production  of  zinc  carbon- 
ate as  a  pigment  or  a  filler.  The  interaction  of  nitre-cake  and 
scrap  metals  is  a  proposal  for  hydrogen  production  involving  the 
consumption  of  cheap  by-products. 


Chapter  X. 
The  Purification  and  Testing  of  Hydrogen. 

The  purification  of  commercial  hydrogen  is  as  important  a 
section  of  hydrogen  technology  as  the  generation  of  the  gas  in 
quantity.  This  is  so  because,  in  the  majority  of  uses  to  which 
the  gas  is  put,  the  absence  of  certain  impurities  is  essential. 
Thus,  for  example,  in  ammonia  synthesis,  traces  of  oxygen,  car- 
bon monoxide  and  water  vapor  exercise  a  very  adverse  effect  on 
the  synthetic  operation  when  iron  or  iron-molybdenum  catalysts 
are  used.  In  the  hydrogenation  of  oils,  the  reaction  velocity  of 
the  hardening  process  is  markedly  decreased  by  the  presence  of 
"poisons"  such  as  sulphides  and  carbon  monoxide x  and  by  dilu- 
ents such  as  nitrogen,  carbon  dioxide  and  hydrocarbons.2  In  the 
reduction  of  tungsten  and  in  the  evacuation  of  electric  filament 
lamps,  absence  of  carbon  compounds  is  desirable  so  as  to  mini- 
mize the  presence  of  carbides  in  the  metallic  product.  This  also 
holds  in  the  case  of  the  fusion  and  working  of  the  platinum 
metals. 

Extended  investigation  will  doubtless  show  that,  by  modifica- 
tion of  the  catalytic  agent  or  of  the  operating  conditions,  catalytic 
hydrogenation  may  be  carried  out  with  hydrogen  not  so  rigor- 
ously purified  as  is  that  now  employed  in  the  majority  of  cases. 
The  use  of  water  gas  as  reducing  agent  in  the  catalytic  reduction 
of  nitrobenzene  in  the  vapor  phase,  the  employment  of  "lique- 
faction process"  hydrogen  in  certain  fat  hardening  works  are 
examples  of  efforts  in  that  direction.  In  such  cases,  the  eco- 
nomic balance  will  be  struck  between  the  expense  of  purification 
on  the  one  hand  and  the  lowered  efficiency  incidental  to  the  use 
of  the  less  pure  product  on  the  other  hand. 

The  main  impurities  in  industrial  hydrogen  prior  to  the 
carrying-out  of  special  purification  are  hydrogen  sulphide,  car- 

»Maxted.  Trans.  Faraday  Soc.,  Dec.,  1917.  Thomas.  J.  Soc.  Chem.  Ind.f 
1920,  89,  10  T. 

'Thomas,  loc.  cit.  Armstrong  and  Hilditch,  J.  Soc.  Chem.  Ind.,  1920,  59, 
120  T.  Proc.  Roy.  Soc.f  1920,  98 A  34. 

171 


172 


INDUSTRIAL  HYDROGEN 


bon  sulphur  compounds,  carbon  dioxide,  carbon  monoxide,  hydro- 
carbons, nitrogen  and  water  vapor.  The  number  and  amounts 
of  these  impurities  present  in  any  given  technical  product  varies 
with  the  method  of  production  and  the  efficiency  with  which  the 
operation  of  production  is  conducted.  Thus,  hydrogen  produced 
by  the  steam-iron  processes  has  varied,  in  different  plants  visited 
by  the  writer,  from  97  per  cent  to  99.9  per  cent  hydrogen.  The 
former  is  an  unnecessarily  impure  product,  resulting  from  poor 
supervision  and  control  of  the  plant.  The  latter  represents  a 
product  produced  under  the  strictest  control  and  with  sacrifice 
of  yield  to  purity  of  product.  In  general,  the  product  from  the 
process  is  intermediate  in  quality  but  more  closely  approximat- 
ing the  higher  quality  example. 

To  obtain  a  general  survey  of  the  purification  problem  the 
following  tabulated  data  are  given  referring  to  the  impurities  in 
the  products  obtained  by  the  more  important  processes  detailed  in 
the  preceding  chapters.  The  purification  processes  which  are 
outlined  in  the  following  pages  have  been  worked  out  in  the  main 
with  special  reference  to  one  or  other  of  such  products.  The  fig- 
ures indicated  in  each  case  represent  average  practice  rather  than 
extreme  cases.  The  figures  are  based  on  dry  gases.  Most  of  the 
products,  however,  would  be  saturated  with  water  at  ordinary 
temperatures. 


'P 

8 

o 

Process 

I 

b! 

c£ 

-S 

C  '{3 

1 

1 

B 

1^ 

2^  Q  <u 

'&£"£'% 

11 

5  2 

T3 

5 

1 

w 

•2>  3  a!  .C 

EGGO  ft 

as 

al 

W 

1 

H 

C 

Steam-Iron  .  .  . 

98.5-99 

0.05 

0.5-1 

0.2-0.3 



0-0.25 

.... 

Liquefaction  .  . 

97-97.5 

.... 

.... 

1.7-2.0 



0.85-1.0 



Water-gas   Ca- 

talytic   (after 

92.6 

Traces 

0.25 

2.9 

0.45 

3.75 

Possible 
Traces 

CO2  removal) 

Ditto  with  shift 

96-97 

Tr&CGS 

0.0-0.2 

0.3-0.5 

3-4 

of  equilibrium 

Electrolvtic   . 

99.5-100 

0-0.5 

Purification  from  Sulphur  Compounds 

The  main  sulphur-containing  impurity  in  technical  hydro- 
gen is  hydrogen  sulphide.     Carbon  sulphur  compounds  may  be 


PURIFICATION  AND  TESTING  OF  HYDROGEN     173 

present  in  minimal  quantities.  The  processes  in  which  these 
compounds  require  removal  are  the  steam-iron  process  and  the 
water-gas  catalytic  processes,  together  with  the  various  proc- 
esses starting  from  hydrocarbons,  if  these  contain  sulphur  in 
the  raw  material.  In  the  liquefaction  process,  all  the  sulphur 
compounds  are  removed  either  in  the  initial  purification  process 
prior  to  liquefaction  (see  Chapter  IV)  or  are  frozen  out  during 
the  liquefaction  of  the  carbon  monoxide.  In  the  electrolytic 
process  the  production  of  sulphur-containing  impurities  is  highly 
improbable. 

Owing  to  the  ease  with  which  the  reaction 

CS2  +  2H20  =  C02  +  2H2S 

occurs  in  contact  with  iron  or  iron  oxide  at  temperatures  in  the 
region  of  300°-700°  C.,  the  gases  produced  in  the  steam-iron  proc- 
ess and  in  the  water-gas  catalytic  processes  will  only  contain 
minute  quantities  of  carbon  disulphide.  These  will  be  too  small, 
generally,  to  exercise  any  deleterious  influence  in  the  subsequent 
use  of  the  gas.  For,  in  the  processes  quoted,  the  reaction  produc- 
ing hydrogen  involves  a  large  excess  of  steam  and  the  equilibrium, 
in  the  above  reaction  is  largely  on  the  right  hand  side  of  the 
equation.  Consequently,  the  removal  of  sulphur  compounds  will 
involve  essentially  the  removal  of  sulphuretted  hydrogen.  This 
is  generally  the  first  of  the  impurities  in  hydrogen  to  be  elimi- 
nated. 

The  gas  may  be  removed  from  hydrogen  by  the  same  methods 
which  are  employed  in  gasworks  practice  for  its  removal  from 
coal  gas.  The  purification  is  attained  by  passage  of  the  gases 
containing  sulphuretted  hydrogen  through  purifiers  containing 
moist  oxide  of  iron  or,  in  certain  cases,  moist  lime.  For  hydro- 
gen sulphide  alone  the  former  is  preferable,  but  when  it  is  de- 
sired also  to  eliminate  carbon  dioxide,  lime  is  frequently  em- 
ployed, though  treatment  with  moist  iron  oxide  followed  by 
scrubbing  with  solutions  of  alkalis  is  coming  into  use.  By  what- 
ever method  practised,  the  purification  can  be  carried  to  a  high 
degree  of  completeness. 

For  iron  oxide  treatment,  the  principal  materials  finding  ap- 
plication are  bog  iron  ore,  a  naturally-occurring  hydrated  oxide 
of  iron,  and  various  artificially  prepared  hydrated  ferric  oxides. 
Thus,  "Lux"  a  trade  product  finds  much  favour  and  is  obtained 


174  INDUSTRIAL  HYDROGEN 

from  bauxite  by  fusion  with  soda  and  subsequent  lixivation, 
yielding  a  solution  of  sodium  aluminate  and  a  colloidal  hydrated 
oxide  of  iron.  Absorption  of  the  hydrogen  sulphide  is  generally 
carried  out  in  a  purification  system  consisting  of  closed  boxes 
carrying  trays  of  the  material,  either  iron  oxide  or  lime,  gen- 
erally lightened  by  sawdust  or  similar  substances  making  for 
porosity.  The  arrangement  of  the  purifiers  and  directions  for 
efficient  working  are  well  known  and  can  be  learned  from  a  stand- 
ard gas  works  manual.3  It  must  be  mentioned  that  in  hydrogen 
purification  it  is  not  possible  to  practice  revivification  in  situ  of 
the  spent  oxide  as  is  usual  in  coal  gas  practice.  This  procedure 
consists  in  the  simultaneous  admission  of  the  foul  coal  gas  and 
air  to  the  oxide  box  system  whereby  the  iron  sulphide  obtained 
in  the  purification  process 

Fe203.xH20  +  3H2S  =  Fe2S3  +  (x  +  3)H20 
Fe2S3  =  2FeS  +  S 

is  simultaneously  oxidised  to  sulphur  and  iron  oxide 

2Fe2S3  +  302  =  2Fe203  +  3S2 
4FeS  +  302  =  2Fe203  +  2S2. 

In  this  way  a  system  of  purifiers  in  coal  gas  practice  can  be 
maintained  in  use  for  a  considerably  longer  interval  of  time  than 
is  possible  if  no  air  is  admitted.  For  pure  hydrogen  production 
this  is  not  possible  owing  to  the  nitrogen  and  other  gases  which 
would  thus  enter  the  hydrogen  gas. 

The  low  capacity  which  iron  oxide  boxes  therefore  have,  when 
used  for  purifying  hydrogen,  as  well  as  the  expense  involved  in 
the  charging  and  discharging  of  the  purifier  system,  have 
prompted  efforts  which  have  been  made  to  eliminate  iron  oxide 
box  practice  as  far  as  is  consistent  with  efficient  removal  of  the 
impurity.  Efforts  have  been  made  to  remove  sulphuretted  hydro- 
gen by  scrubbing  with  a  suspension  of  colloidal  iron  oxide  in 
water.  Experiment  has  shown  that  in  this  manner  removal  of 
the  impurity  is  not  complete  4  but  that  a  large  bulk  of  the  hydro- 
gen sulphide  may  be  so  removed.  Economy  of  operation  sug- 
gests, therefore,  a  dual  system  in  which  the  main  bulk  of  the  im- 

*  See,  for  example,  Meade,  "Modern  Gasworks  Practice,"  pp.  384-414.  D.  Van 
Nostrand  Co.,  1916. 

4  Evans,  Gas  Record,  1919,  15,  215;  Qua  Age,  1919,  43,  475.  Chem.  Abat., 
1919,  IS,  1,380. 


PURIFICATION  AND  TESTING  OF  HYDROGEN     175 

purity  is  eliminated  by  the  liquid  scrubber,  the  final  traces  being 
removed  by  the  usual  box  treatment.  In  this  way  a  longer 
duty  without  discharge  can  be  obtained  from  the  boxes.  Ex- 
perimental work  has  recently  established  that  the  power  cost 
on  the  liquid  scrubber  is  but  a  fraction  of  that  involved  in  labor 
on  the  renewal  of  oxide  boxes. 

For  rigorous  elimination  of  traces  of  sulphur  compounds, 
scrubbing  with  iodine  5  and  with  copper  sulphate  solution 6  have 
been  proposed.  With  efficiently  operated  iron  oxide  systems  these 
should  not  be  necessary,  especially  if  the  gases  are  subsequently 
to  be  freed  from  carbon  dioxide  by  scrubbing  with  alkalis. 

The  removal  of  carbon  disulphide  from  hydrogen  is  most  con- 
veniently attained  technically  by  interaction  with  steam  in  pres- 
ence of  a  catalyst,  the  hydrogen  sulphide  formed  by  the  reaction, 

CS2  +  2H20  =  C02  +  2H2S, 

being  then  removed  in  one  or  other  of  the  ways  already  out- 
lined. As  catalytic  agent,  iron  oxide  or  iron  oxide-containing 
catalysts  such  as  are  detailed  in  the  chapter  on  the  water-gas 
catalytic  process,  are  suitable.  The  patent  of  Guillet7  calls  for 
iron  oxide  as  catalyst  and  a  working  temperature  of  80° -200°  C. 
In  such  case,  however,  the  hydrogen  sulphide  is  retained  and,  in 
course  of  use,  the  catalyst  loses  its  activity  owing  to  the  for- 
mation of  iron  sulphide.  Rideal  and  Taylor 8  showed  that, 
by  operating  at  temperatures  above  300°  C.,  the  hydrogen  sul- 
phide was  not  absorbed  by  the  catalyst  which  could  therefore  be 
used  continuously,  the  sulphuretted  hydrogen  formed  being  elimi- 
nated in  a  subsequent  operation.  The  temperature  at  which  hy- 
drogen sulphide  is  no  longer  retained  is  conditioned  in  part  by 
the  concentration  of  steam  in  the  reaction  mixture.  The  same 
authors  showed  that  this  reaction  could  be  conducted  preferen- 
tially, the  reaction  of  steam  with  carbon  disulphide  occurring 
more  readily  than  that  with  carbon  monoxide.  Apparatus  of  the 
type  described  for  the  water-gas  catalytic  process  is  suitable  also 
for  this  interaction  of  steam  and  carbon  disulphide. 

The  Badische  Co.  (B.  P.  14,509/1913),  showed  that  carbon 
disulphide  could  be  eliminated  from  hydrogen  by  passage  of  the 

5U.  S.  P.  1,034,646/1912. 

•  D.  R.  P.  286,374/1914. 
*B.  P.  18,597/1912. 

•  B.  P.  130,654/1919. 


176  INDUSTRIAL  HYDROGEN 

gas,  at  pressures  above  5  atmospheres,  through  hot  solutions  of 
sodium  hydroxide.  As  example,  a  10-25  per  cent  solution  at  a 
temperature  of  150°-225°  C.  under  a  pressure  of  50  atmospheres 
was  cited.  The  technical  operation  of  this  process  is  needlessly 
complex  unless  other  objects  are  simultaneously  to  be  achieved. 
The  Badische  Co.  used  this  treatment  originally  for  the  removal 
of  carbon  monoxide  and  it  was  found  that  carbon  disulphide  was 
removed  at  the  same  time. 

Carbon  disulphide  may  be  removed  by  processes  of  catalytic 
decomposition  in  presence  of  hydrogen 

CS2  +  2H2  =  C  +  2H2S. 

As  catalytic  agents  platinum,  nickel,  bauxite,  fireclay,  pumice 
and  iron  oxide  are  suitable,9  nickel  having  been  used  for  the  re- 
moval of  carbon  disulphide  from  coal  gas  on  a  large  scale.  Com- 
plete removal  of  the  impurity  is  only  attainable,  however,  at 
very  elevated  temperatures,  so  that  the  process  would  be  less  ap- 
plicable to  the  case  of  hydrogen  than  the  treatment  with  steam 
already  discussed.  In  the  case  of  coal  gas,  where  the  presence 
of  carbon  monoxide  may,  without  special  and  careful  control, 
give  rise,  with  steam,  to  carbon  dioxide  production,  the  utility  of 
this  reaction  with  hydrogen  is  more  apparent.  The  gradual  de- 
terioration of  the  catalyst  by  deposition  of  the  resulting  carbon  in 
the  contact  mass  constitutes  an  additional  disadvantage  of  the 
process.  In  practice  this  must  be  burnt  off  at  intervals  and  the 
contact  mass  freshly  reduced.  It  is  not  surprising  therefore  that, 
as  yet,  this  method  of  removal  of  carbon  disulphide  has  not  come 
into  use  in  hydrogen  purification. 

The  removal  of  carbon  disulphide  by  cooling  the  gases  to 
— 190°  C.  has  been  previously  mentioned,  the  patent  claims  of 
Bedford  and  Williams  10  specially  referring  to  this  process.  This 
method  of  removal  also  eliminates  thiophene,  a  compound  which 
is  not  removable,  or  only  with  difficulty,  by  the  other  methods 
outlined. 

Purification  from  Carbon  Dioxide 

The  method  of  removal  of  carbon  dioxide  from  hydrogen 
varies  with  the  quantity  of  the  impurity  present  in  the  gas.  For 

•Carpenter,  J.  Gas  Lighting,  1914,   126,  928.     Evans,  J,   Soc.   Chem.  Ind., 
1915,  34,  9.     Berk  &  Co.,  and  Hood  B.  P.  143,641/1919. 
10  B.  P.  3,752/1910. 


PURIFICATION  AND  TESTING  OF  HYDROGEN     177 

gases  with  a  percentage  of  carbon  dioxide  lower  than  3  per  cent, 
the  most  convenient,  and  probably  the  most  economical,  methods 
of  removal  utilise  caustic  alkali  solutions  or  moist  lime  as 
absorption  agent.  With  higher  concentrations  of  carbon  dioxide 
present,  the  expense  of  alkali  absorption  agents  becomes  ex- 
cessive and  use  is  made  of  water,  alcohol  or  alkali  carbonate 
solutions  as  solvent  for  the  gas,  compression  of  gas  and  solvent 
being  used  as  an  auxiliary  in  the  process.  Aqueous  ammonia 
solutions  have  also  been  suggested  as  absorption  agents,  the  am- 
monium carbonate  solutions  formed  in  the  process  being  subse- 
quently heated  to  90°  C.,  at  which  temperature  the  carbon  di- 
oxide may  be  expelled  without  marked  loss  of  ammonia.  Re- 
cent developments  point  to  the  combination  of  the  water-gas 
catalytic  process  with  the  ammonia-soda  process,  in  which  case 
the  carbon  dioxide  would  be  removed  from  the  hydrogen  by  the 
ammonia  entering  the  ammonia-soda  cycle. 

A  purifier  system,  composed  of  rectangular  boxes  partially 
filled  with  hydrated  lime  arranged  on  shelves,  is  the  usual  appara- 
tus in  English  practice  for  carbon  dioxide  removal  from  steam- 
iron  process  hydrogen  containing  0-3  per  cent  of  the  impurity. 
The  procedure  was  standard  practice  in  the  coal-gas  industry  in 
former  times  and  specifications  of  plant  required  are  to  be  found 
in  manuals  of  gas  works  practice.  Thus,  Meade ai  suggests  that 
the  lime  used  should  contain  about  30  per  cent  of  water  in  ex- 
cess of  that  required  to  form  the  hydroxide.  The  depth  of  layer 
should  be  about  8  inches,  to  prevent  the  formation  of  channels 
in  the  material,  thus  avoiding  the  escape  of  untreated  gas.  With 
this  depth  of  material  and  a  set  of  four  purifier  boxes,  an  allow- 
ance of  0.7  square  foot  of  area  per  box  per  1,000  cubic  feet  of 
gas  to  be  purified  per  day  is  sufficient  in  coal-gas  technology. 
In  view  of  the  more  rigorous  requirements  in  the  case  of  hydrogen, 
increase  of  this  figure  to  1.0  square  foot  would  not  be  excessive. 
In  this  type  of  purifier,  as  in  the  case  of  iron  oxide  box  purifiers, 
the  labor  and  renewal  charges  are  high.  American  practice  has 
therefore  replaced  moist  lime  absorption  systems  with  a  scrubber 
system  using  sodium  hydroxide  solutions. 

Scrubbers  suitable  for  this  purpose  consist  of  cylindrical 
towers  down  which  flows  the  caustic  alkali  solutions  over  coke 
or  other  filling  material,  the  gas  passing  upwards  and  counter- 

"Loc.  clt.,    p.  174. 


178  INDUSTRIAL  HYDROGEN 

current  to  the  liquid  flow.  The  rates  of  gas  and  liquid  flow  will 
obviously  be  governed  by  the  carbon  dioxide  concentration.  Ordi- 
nary water  scrubber  practice  suggests  the  approximate  capacity 
of  tower  space  required. 

Specifications  for  the  removal  of  large  concentrations  of  car- 
bon dioxide  by  processes  of  pressure  water  washing  have  already 
been  given  (Chapter  III).  The  use  of  alcohol  in  place  of  water, 
suggested  by  Bedford,  would  seem  to  be  excluded  technically  on 
the  score  of  cost.  By  either  process,  there  appears  to  be  residual 
amounts  of  carbon  dioxide  (0.1  —  1%)  remaining  in  the  gas, 
which  are  subsequently  removed  by  scrubbing  with  aqueous  al- 
kalis. Claude 12  proposed  to  substitute  lime  water  for  water  in 
the  counter-current  pressure  washing  system  thus  ensuring  com- 
plete removal  of  the  impurity.  The  complications  thereby  in- 
troduced owing  to  separation  of  calcium  carbonate  would  seem  to 
offset  the  advantages  thus  obtained. 

The  employment  of  solutions  of  alkali  carbonates  (of  which 
potassium  carbonate  would  be  preferable  owing  to  its  greater 
solubility)  is  not  a  practicable  proposal  for  purification  of  hy- 
drogen from  carbon  dioxide  if  increased  pressures  are  not  em- 
ployed. This  is  due  to  the  slow  rate  of  absorption  of  the  gas  at 
ordinary  gas  pressure  when  the  concentration  is  decreased  and 
also  to  the  incompleteness  of  the  removal.  In  the  manufacture 
of  carbon  dioxide  from  exhaust  and  flue  gases  by  absorption  in 
alkali  carbonate  solutions  and  subsequent  decomposition  of  the 
bicarbonate  liquor,  only  about  one-half  of  the  carbon  dioxide 
present  in  the  original  gas  mixture  is  recovered,  the  rest  passing 
to  waste.  The  inapplicability  of  the  process  to  hydrogen  puri- 
fication in  such  a  form  is  therefore  manifest.  When  pressure  is 
employed  the  use  of  alkali  carbonates  instead  of  water  seems 
less  preferable  owing  to  the  cost  involved  in  regeneration  of  the 
liquor. 

Purification  from  Carbon  Monoxide 

The  various  types  of  industrial  hydrogen  containing  carbon 
monoxide  are  broadly  divisible  into  two  classes,  those  in  which 
concentrations  of  the  impurity  range  from  0  to  0.5  per  cent,  and 
those  in  which  the  carbon  monoxide  concentration  reaches  2  to  4 
per  cent.  Steam-iron  process  hydrogen  is  typical  of  the  former. 

"B.  P.  15,053/1914. 


PURIFICATION  AND  TESTING  OF  HYDROGEN     179 

Hydrogen  by  the  Griesheim-Elektron  Co.'s  process  would  also 
fall  in  this  category  if  technically  operated.  The  continuous 
water-gas  catalytic  process,  the  "liquefaction"  process  and  proc- 
esses of  thermal  decomposition  of  hydrocarbons  yield  hydrogen 
containing  the  upper  range  of  carbon  monoxide  concentrations. 
Certain  purification  processes  have  particular  application  in  re- 
spect to  only  one  or  other  of  the  two  types.  Other  processes  are 
equally  applicable  to  both. 

Conversion  to  Methane. — The  catalytic  hydrogenation  of  car- 
bon monoxide  to  yield  methane  is  a  method  of  purification  which 
would,  in  general,  be  confined  to  gases  containing  the  lower  range 
of  concentration.  The  reaction, 

CO  +  3H2  =  CH4  +  H20, 

gives  rise  to  methane  which  is  itself  difficult  to  remove.  In  the 
majority  of  uses  to  which  hydrogen  is  put,  methane  is  an  inert 
constituent,  but,  in  circulatory  processes,  such  inert  constituents 
accumulate  and  necessitate  loss  of  hydrogen  by  purging.  Fur- 
thermore, since  three  volumes  of  hydrogen  are  consumed  in  the 
removal  of  one  volume  of  carbon  monoxide  a  fiaaterial  hydrogen 
loss  would  occur  in  the  treatment  of  gases  containing  2-4  per 
cent  carbon  monoxide.  Use  of  the  methanation  process  is  there- 
fore generally  limited  to  the  elimination  of  traces  of  the  im- 
purity. 

In  this  application  the  methanation  process  is  extremely  valu- 
able. Thex  reaction  proceeds  rapidly  and  quantitatively  at 
300°  C.,  in  presence  of  a  nickel  catalyst.  The  contact  mass  is 
cheap,  a  suitable  material  being  readily  prepared  by  soaking 
a  silica  brick  material,  such  as  Nonpareil  brick,  broken  to  suit- 
able size,  in  a  solution  of  nickel  nitrate  of  such  a  strength  that 
on  withdrawing  from  the  liquor  and  drying  off,  the  content  of 
the  resulting  material  is  10  per  cent  with  respect  to  metallic 
nickel.  The  nickelised  brick  so  obtained  is  placed  in  position 
in  the  catalyst  chamber  and  heated  to  300°  C.  in  an  atmosphere 
of  hydrogen.  After  the  evolution  of  nitrogen  oxides  and  ammonia 
has  ceased,  the  material  is  in  an  active  form  for  the  methanation 
process.  An  active  material  will  eliminate,  quantitatively,  car- 
bon monoxide  from  1,000  times  its  own  apparent  volume  of  hy- 
drogen per  hour  at  300°  C.,  if  the  carbon  monoxide  concentration 
does  not  exceed  0.5  per  cent. 


180  INDUSTRIAL  HYDROGEN 

The  gas  to  be  treated  by  such  a  purification  process  must  be 
rigorously  freed  from  sulphur  compounds  in  a  prior  operation. 
Otherwise,  the  activity  of  the  catalytic  agent  shows  a  steady  de- 
terioration with  use.  Steam-iron  process  hydrogen  which  has  re- 
ceived iron  oxide  box  treatment  and  then  treatment  for  removal 
of  carbon  dioxide  is  sufficiently  pure  for  purification  from  carbon 
monoxide  according  to  this  process.  The  hydrogenation  process 
may  also  be  used  at  the  same  temperature  for  the  removal  of 
carbon  dioxide,  the  reaction  being 

C02  +  4H2  =  CH4  +  2H20. 

It  is  obvious,  however,  that  this  would  be  expensive  as  4  volumes 
of  hydrogen  are  consumed  per  volume  of  carbon  dioxide.  Since 
the  latter  is  also  present  in  steam-iron  process  hydrogen  to  the 
extent  of  1  per  cent  or  more,  there  would  be  a  correspondingly 
large  percentage  of  methane  in  the  product.  For  this  reason  the 
carbon  dioxide  will  normally  be  removed  from  the  gas  prior  to 
the  hydrogenation  or  methanation  process. 

The  Harger-Terry  Process  of  Preferential  Combustion. — This 
recent  process13  for  purifying  hydrogen  from  carbon  monoxide 
makes  use  of  the  discovery  that,  in  presence  of  suitable  contact 
agents,  carbon  monoxide  is  more  readily  oxidised  than  hydrogen. 
The  process  is  peculiarly  suited  to  hydrogen  containing  0-0.5  per 
cent  of  the  impurity.  It  has  advantages  over  the  preceding 
process  in  that  the  preferential  combustion  process  may  readily 
be  conducted  in  presence  of  carbon  dioxide,  the  product  of  re- 
action, moreover,  being  carbon  dioxide,  the  whole  of  which  may 
then  be  removed  by  the  usual  absorption  processes.  No  accumu- 
lation of  inert  gas  need,  therefore,  arise. 

Metallic  oxides  and  mixtures  of  the  same  form  the  most  suit- 
able catalysts  for  the  preferential  combustion  process.  With  a 
definite  catalyst  there  is  a  definite  interval  of  temperature  within 
which  the  oxygen  present  in  a  hydrogen-carbon  monoxide-oxygen 
mixture  is  consumed  mainly  by  the  carbon  monoxide.  This  in- 
terval is  about  50°  C.  Thus,  by  taking  hydrogen  with  a  carbon 
monoxide  content  of  0.5  per  cent,  and  adding  0.5  per  cent  oxygen 
(equal  to  twice  the  theoretical  quantity  required  by  carbon  mon- 
oxide) the  gas  mixture  may  be  freed  from  carbon  monoxide  by 
passage  of  the  gas  over  a  suitable  preferential  combustion  cat- 

»B.  P.  127,609/1917. 


PURIFICATION  AND  TESTING  OF  HYDROGEN    181 

alyst,  maintained  within  the  right  interval  of  temperature.  The 
excess  oxygen  not  utilised  by  the  carbon  monoxide  will  be  used 
by  the  hydrogen  or  may,  in  part,  pass  on  unchanged. 

The  principal  catalysts  from  the  point  of  view  of  technical 
operation  are  copper  oxide  and  iron  oxide,  alone  or  admixed  with 
other  oxides.  Copper  oxide  and  mixtures  with  other  oxides,  for 
example,  manganese  dioxide,  are  active  in  the  neighbourhood  of 
100°  C.  Iron  oxide  or  mixtures  of  iron,  and  chromium  oxides 
or  mixtures  of  iron,  chromium  and  cerium  oxides  are  active  in 
the  temperature  interval  of  200°-300°  C.  With  such  catalysts, 
suitably  prepared,  hydrogen  may  be  freed  from  concentrations  of 
carbon  monoxide  up  to  0.5  per  cent  with  the  consumption  of 
oxygen  equal  to  a  100  per  cent  excess  over  that  required  by  the 
carbon  monoxide  alone.  The  oxygen  needed  for  the  preferential 
combustion  process  is  best  supplied  by  means  of  electrolysis  of 
aqueous  alkalis,  the  hydrogen  simultaneously  produced  being 
used  to  supplement  the  main  supply  of  the  gas  after  purification. 

This  process  of  preferential  combustion  has  proved  specially 
adaptable  to  the  purification  of  steam-iron  process  hydrogen 
from  carbon  monoxide;  trials  on  a  large  experimental  scale  have 
proved  very  successful  and  adaptation  to  technical  operation  is 
now  being  undertaken.  The  gas  to  be  purified  is  first  freed 
from  hydrogen  sulphide  by  iron-oxide  box  purification.  It  is  then 
mixed  with  about  20  per  cent  by  volume  of  steam  and  with 
oxygen  in  quantity  calculated  as  sufficient  for  oxidation  of  twice 
the  amount  of  carbon  monoxide  present.  The  steam  acts  protec- 
tively in  restricting  hydrogen  combustion  and  also  prohibits  re- 
duction of  iron  oxide  catalysts.  The  mixed  gases  are  passed 
through  a  catalyst  chamber  containing  the  oxides  on  trays,  the 
temperature  being  carefully  regulated  to  attain  the  maximum 
preferential  effect.14  The  exit  gases  are  next  freed  from  steam 
in  a  scrubber  and  then  passed  to  the  carbon  dioxide  purification 
system.  By  this  process  it  has  been  shown  possible  on  the  tech- 
nical scale  to  remove  more  than  95  per  cent  of  the  carbon  mon- 
oxide from  steam-iron  process  hydrogen  averaging  0.4  to  0.5  per 
cent  carbon  monoxide  with  a  maximum  hydrogen  loss  of  0.5  per 
cent. 

Without  modification,  the  preferential  combustion  process  is 
not  readily  applicable  to  hydrogen  gas  containing  the  higher  con- 

"  See  Rideal,  J.  Chem.  8oo.t  1919,  115,  995. 


182  INDUSTRIAL  HYDROGEN 

centrations  of  carbon  monoxide,  2  to  4  per  cent.  Several  reasons 
are  involved.  The  most  important  reason  relates  to  the  thermal 
problem  in  question.  The  preferential  nature  of  the  oxide  cat- 
alysts is  generally  restricted  to  a  temperature  interval  of  about 
50°  C.  Copper  oxide  which  will  act  as  catalyst  to  oxidise  carbon 
monoxide  on  hydrogen  at  120°  C.,  will  normally  act  as  catalyst 
for  the  combustion  of  hydrogen  and  oxygen  at  170°  C.  Now  the 
heats  of  oxidation  of  carbon  monoxide  and  hydrogen 

CO  +  V202  —  C02  +  68,000  calories, 
H2  +  YA  =  H20  +  58,000  calories, 

are  sufficiently  great  to  raise  the  temperature  of  a  reaction  mix- 
ture in  which  one  per  cent  of  either  gas  is  oxidised  by  about 
100°  C.  The  preferential  nature  of  the  combustion  is  destroyed 
and  hydrogen,  by  reason  of  its  concentration  alone,  combines 
with  the  bulk  of  the  oxygen.  This  difficulty  could  be  overcome 
by  arranging  a  cyclic  operation  in  which  the  incoming  gas  of  high 
carbon  monoxide  content  could  be  diluted  with  the  requisite 
amount  of  already  purified  gas  to  make  an  entering  gas  with  a 
carbon  monoxide  concentration  not  exceeding  0.5  per  cent.  With 
such  a  procedure,  however,  it  is  apparent  that  by  allowing  an  ex- 
cess of  oxygen  equivalent  to  that  required  by  the  carbon  mon- 
oxide, the  loss  of  hydrogen,  in  a  gas  containing  3  per  cent  of  the 
impurity,  will  also  be  3  per  cent.  The  expense  of  the  process 
in  hydrogen  alone  would  become  marked. 

Rideal  and  Taylor 15  proposed  to  obviate  these  difficulties  by 
operating  a  combined  process  of  interaction  with  steam  and 
preferential  combustion  on  gases  containing  2-4  per  cent  of  car- 
bon monoxide.  The  procedure  recommended  is  to  mix  the  gas, 
from  which  sulphur  compounds  have  been  removed,  with  one  half 
its  volume  of  steam  and  to  pass  the  gas  over  a  water-gas  catalyst 
(see  page  68)  at  a  temperature  of  400°-450°  C.  In  this  way 
by  means  of  the  reaction 

CO  +  H20  =  C02  +  H2 

the  concentration  of  carbon  monoxide  is  reduced  at  the  expense 
of  the  steam,  approximately  to  the  equilibrium  concentration 
at  the  temperature  stated.  In  this  way,  the  carbon  monoxide  con- 
centration in  the  issuing  gas  is  diminished  to  less  than  0.5  per 

16  B.  P.  129,743/1918. 


PURIFICATION  AND  TESTING  OF  HYDROGEN     183 

cent.  On  lowering  the  temperature,  adding  oxygen  and  passing 
once  more  over  a  catalyst  containing  iron  oxide  at  250°  C.  this 
residual  impurity  can  be  converted  to  carbon  dioxide  practically 
quantitatively.  Experiments  on  a  technical  hydrogen  made  by 
the  liquefaction  process  and  on  the  product  of  the  water-gas 
catalytic  process  after  carbon  dioxide  removal,  established  the 
practicability  of  this  procedure.  The  necessity  for  a  two-stage 
operation  which  this  involves  naturally  makes  the  process  more 
expensive  than  the  simple  procedure  applicable  to  steam-iron 
process  hydrogen. 

Investigations  on  the  oxidation  of  carbon  monoxide  in  air  for 
gas-mask  purposes  conducted  by  the  Chemical  Warfare  Service 16 
showed  the  possibility  of  obtaining  catalysts  for  carbon  monoxide 
oxidation  operative  at  ordinary  temperatures.  In  hydrogen,  these 
catalysts  also  function  preferentially,  but,  owing  to  the  poisoning 
effect  of  water-vapor  on  the  low  temperature  catalysts,  it  is  found 
that  operation  at  ordinary  temperatures  is  not  readily  possible. 
Temperatures  in  the  neighbourhood  of  100°  C.  are  adequate  to 
overcome  this  adverse  effect  of  water  vapor.  Thus  far,  the  proc- 
ess has  not  been  operated  successfully  on  any  large  scale  with 
hydrogen  containing,  in  addition  to  carbon  monoxide,  a  large  pro- 
portion of  carbon  dioxide,  for  example  30  per  cent  (see  Chapter 
III,  p.  74).  The  elimination  of  carbon  monoxide  in  presence  of 
such  large  quantities  of  carbon  dioxide  would  represent  a  con- 
siderable step  forward. 

Purification  by  Reaction  with  Soda-Lime  or  Lime. — Carbon 
monoxide  reacts  with  soda-lime  at  temperatures  of  180°  C.  and 
upwards.  The  reaction  proceeds  in  presence  of  hydrogen,  so  that 
it  may  be  used  for  purposes  of  purification.  At  the  lower  tem- 
peratures in  question,  sodium  formate  is  produced,  but  reaction 
velocity  is  slow.  Consequently,  pressure  may  be  employed  to 
facilitate  reaction.  At  higher  temperatures  reaction  also  occurs, 
but,  owing  to  decomposition  of  the  formate,  hydrogen  and  carbon 
dioxide  are  formed.  Consequently,  the  soda  is  gradually  con- 
verted to  carbonate. 

Lime,  employed  at  500°  C.,  gives  hydrogen  and  carbon  dioxide 
from  moist  hydrogen  containing  traces  of  carbon  monoxide. 
Steam  favors  the  reaction  and  the  efficiency  of  carbon  monoxide 

"Lamb,  Bray  and  Frazer,  J.  Ind.  Eng.  Ghent. ,  1920,  12,  213. 


184  INDUSTRIAL  HYDROGEN 

removal  is  determined  by  the  water-gas  reaction.  Iron  oxide 
catalysts  assist  the  process.  The  data  already  given  in  reference 
to  the  Griesheim  Elektron  process  are  applicable  also  to  the 
case  of  purification  with  lime.  Experiment  shows  that,  at  500°  C., 
in  presence  of  lime  and  an  iron  activator,  hydrogen  containing  2 
per  cent  carbon  monoxide  will  be  converted  to  a  hydrogen  carbon- 
dioxide  mixture  containing  less  than  0.1  per  cent  carbon  monoxide 
in  a  single  passage.  The  process  suffers  from  the  same  disad- 
vantages as  the  Greisheim  Elektron  process  (q.v.)  and  requires 
a  high  temperature  of  operation. 

Purification  by  Aqueous  Alkalis  Under  Pressure. — The  re- 
moval of  carbon  monoxide  from  hydrogen  by  interaction  of  the 
impurity  with  alkalis  to  form  formates  can  be  very  effectively 
carried  out  by  the  use  of  solutions  of  the  alkali  at  high  tem- 
peratures, the  prevailing  pressure  being  sufficiently  great  to  per- 
mit the  necessary  superheating  of  the  solution.  Thus,  carbon 
monoxide  in  an  original  concentration  of  2-4  per  cent,  such  as  oc- 
curs in  the  continuous  water-gas  catalytic  process  and  in  the 
liquefaction  process,  can  be  reduced  to  a  concentration  of  less 
than  0.1  per  cent  by  passage  through  a  solution  of  sodium  hy- 
droxide at%a  temperature  of  250°  C.,  the  gas  pressure  employed 
exceeding  50  atmospheres.  The  reaction  occurring  is  expressible 
by  means  of  the  equation: 

NaOH  +  CO  =  HCOONa. 

This  process  was  originally  employed  by  the  Badische  Co.  for 
the  purification  of  the  hydrogen  used  for  ammonia  synthesis. 
The  patents  relating  to  the  same 17  call  for  the  use  of  80  per  cent 
sodium  hydroxide  solutions  at  50  atmospheres  pressure  and 
260°  C.,  as  well  as  the  use  of  25  per  cent  solutions  at  200  atmos- 
pheres pressure  and  240°  C.  The  higher  concentration  is  techni- 
cally unsuitable  owing  to  separation  of  the  solid  product  of  re- 
action.18 

It  is  obvious  that  the  technical  difficulties  associated  with 
the  conduct  of  such  a  purification  process  are  very  great.  Experi- 
ments on  a  small  scale  show  that  the  reaction  is  not  rapid  and  is 
determined  by  the  rate  of  solution  of  the  carbon  monoxide  in  the 

17  B.    P.    1,759/1912;    Fr.    P.    439,262/1912;    U.    S.    P.    1,126,371/1915    and 
1,333,087/1915. 

18  See    also,    Weber,    Dissertation,    Karlsruhe,    1906 ;    Fonda,    Dissertation, 
Karlsruhe,  1908,  for  further  data  on  the  action  of  carbon  monoxide  on  alkalis. 


PURIFICATION  AND  TESTING  OF  HYDROGEN     185 

liquor.  Consequently,  acceleration  of  the  reaction  is  brought 
about  if  the  gas  can  be  introduced  into  the  absorbing  liquor  in 
as  finely  divided  state  as  possible  and  at  as  high  a  pressure  as 
possible.  Alternatively,  introduction  of  liquor  in  the  "atomised" 
condition  into  the  compressed  gas  space  also  makes  for  accelera- 
tion of  reaction.  The  temperatures  and  pressures  requisite,  how- 
ever, render  such  devices  difficult  of  achievement.  Indeed,  the 
operation  of  lifting  the  liquor  to  the  top  of  an  absorption  tower 
so  that  it  may  flow  counter-current  to  a  gas  stream  is  attended 
with  difficulties  of  an  engineering  nature  which  are  by  no  means 
slight. 

It  is,  therefore,  not  surprising  that  this  method  of  purifica- 
tion has  been  displaced  by  others  in  which  the  technical  diffi- 
culties are  less  pronounced.  The  sodium  formate  which  results 
from  the  process  is  a  valuable  product  up  to  the  prevailing  ca- 
pacity of  the  market.  The  early  operations  of  the  Badische  Co., 
however,  created  such  a  surplus  of  the  formate  that  a  market  for 
the  whole  of  it  was  found  with  difficulty. 

Assuming  no  market  for  the  formate,  the  process  becomes 
expensive  because  caustic  soda  is  consumed,  and,  since  sodium 
formate  on  decomposition  yields  carbonate,  causticisation  is  nec- 
essary before  the  salt  can  be  turned  back  into  the  purification 
system.  The  high  pressures  necessary  for  the  conduct  of  the 
process  eliminate  it  from  consideration  in  all  cases  except  those 
in  which  hydrogen  at  high  pressures  is  consumed.  For  high 
pressure  hydrogen,  the  technique  of  the  cuprous  ammonium  salt 
solution  process  next  to  be  described  is,  relatively,  so  much  sim- 
pler that  it  has  superseded  the  process  of  absorption  by  aqueous 
alkalis. 

Purification  by  Absorption  in  Ammoniacal  Cuprous  Salt  Solu- 
tions.— This  process,  which  was  the  method  finally  adopted  by 
the  Badische  Co.,  for  the  purification  of  hydrogen  from  carbon 
monoxide  for  use  in  the  synthetic  ammonia  process,  is  based  on 
the  well  known  reaction  between  carbon  monoxide  and  am- 
moniacal  cuprous  salts  solutions  which  forms  the  basis  of  carbon 
monoxide  estimation  in  ordinary  gas  analysis.  Carbon  monoxide 
is  slowly  absorbed  by  such  solutions  with  the  formation  of  cop- 
per ion  complexes  containing  carbon  monoxide  as  illustrated  by 
the  equations: 


186  INDUSTRIAL  HYDROGEN 

CuCl  +  NH3  =  (Cu.NH3)Cl 
(Cu.NH3)Cl  +  CO  =  (Cu.NH3.CO)Cl. 

The  proposal  to  remove  carbon  monoxide  from  technical  gases 
by  this  method  was  first  made  by  Huntingdon  (B.  P.  15,310/ 
1884) ,  the  gas  specified  being  producer  gas  and  the  action  being 
intensified  by  the  use  of  pressure  both  on  gas  and  liquid.  The 
copper  solution  after  use  was  to  be  regenerated  by  subjecting  it 
to  a  vacuum,  whereby  the  carbon  monoxide  was  evolved.  Similar 
claims  are  embodied  in  Williams'  patent 19  and  in  the  patent  to 
Linde.20  On  trial,  the  Badische  Co.  found  that  the  utility  of  the 
process  was  marred  by  the  solutions  employed  attacking  the 
iron.  Special  patent  claims  were  therefore  made  for  particular 
solutions  in  which  this  adverse  feature  is  eliminated.  Thus,  one 
patent 21  provides  for  the  presence  in  the  copper  solution  of  at 
least  6  per  cent  of  free  ammonia  or  ammonium  carbonate,  for 
use  in  steel  vessels  under  pressure.  Later  patents  call  for  the 
elimination  of  halogens  entirely  22  the  halogen  being  replaced  by 
weak  acids  such  as  formic  and  acetic  acid.  It  is  probably  that 
ammoniacal  cuprous  formate  was  used  as  the  absorption  liquor  on 
the  technical  scale  in  Germany  in  recent  years.  In  the  patent  to 
the  General  Chemical  Co.  and  De  Jahn23  the  salt  employed  is 
the  carbonate  and  is  prepared  by  circulating  a  mixture  of  'air  and 
ammonium  carbonate  over  pure  copper  until  the  requisite  cupric 
ion  concentration  is  attained,  after  which,  the  solution  is  circu- 
lated in  absence  of  oxygen  until  the  cupric  ion  is  reduced  to  the 
cuprous  condition. 

Employed  at  200  atmospheres  pressure,  an  ammoniacal  cu- 
prous salt  solution  will  absorb  from  hydrogen  any  oxygen  that 
may  be  present,  any  residual  carbon  dioxide,  by  combination  with 
the  ammonia  present,  and  finally,  practically  all  of  the  carbon 
monoxide  present  in  a  gas  containing  2-5  per  cent  of  this  impur- 
ity. The  residual  carbon  monoxide  concentration  with  efficient 
working  of  the  process  is  less  than  0.1  per  cent.  It  is  seldom 
below  0.01  per  cent. 

The  quantity  of  solution  required  varies  with  the  average  con- 
centration of  the  impurity,  with  the  strength  of  copper  solution 

19  B.  P.  19,096/1889. 

20  D.  R.  P.  289,106/1914. 

21  B.  P.  8,030/1914. 

22  B.  P.  9,271/1914  and  20,616/1914  ;  compare  also  TJ.  S.  P.  1,196,101/1916. 

23  B.  P.  120,546/1918. 


PURIFICATION  AND  TESTING  OF  HYDROGEN     187 

employed  and  with  the  prevailing  gas  pressure.  Thus,  a  solution, 
one  volume  of  which  at  200  atmospheres  pressure  will  absorb  20- 
30  volumes  of  carbon  monoxide  will  absorb  4-5  volumes  of  the 
gas  at  a  gas  pressure  of  10  atmospheres.  It  is  thus  apparent  that 
the  absorption  is  not  a  simple  case  of  Henry's  Law,  but,  on  the 
contrary,  a  question  of  a  decomposition  equilibrium  in  the  case 
of  a  carbonyl  ion  complex.  Satisfactory  removal  of  the  carbon 
monoxide  is  obtained  in  technical  practice  if  provision  is  made  for 
a  15  minute  period  of  contact  between  gas  and  absorbing  liquid. 
This  is  generally  attained  in  steel  towers  packed  with  a  suitable 
packing  material,  the  absorbing  liquor  being  delivered  at  the  pre- 
vailing pressure  to  the  top  of  the  towers  and  flowing  downwards 
counter-current  to  the  gas  passing  upwards.  For  the  German 
plants,  steel  towers,  10  metres  high,  similar  to  those  used  for  re- 
moval of  carbon  dioxide,  were  in  use,  at  a  working  pressure  of  200 
atmospheres. 

In  a  recent  study,  by  Hainsworth  and  Titus,24  of  the  problem 
of  carbon  monoxide  absorption  using  cuprous  ammonium  carbon- 
ate solutions,  it  was  shown  that  the  absorption  capacity  of  a 
solution  having  a  given  cuprous  copper  content  was  a  function  of 
several  variables.  It  is  dependent  on  the  free  ammonia  content 
of  the  solution  and  on  the  partial  pressure  of  carbon  monoxide 
above  it  as  well  as  on  the  concentration  of  cuprous  copper.  The 
absorption  takes  place  due  to  the  formation  of  an  unstable  com- 
pound in  solution,  probably  containing  one  mole  of  carbon  mon- 
oxide per  gram  atom  of  cuprous  copper.  This  corresponds  ap- 
proximately to  0.2  pounds  of  copper  per  cubic  foot  of  carbon  mon- 
oxide. Cupric  copper  is  reduced  to  cuprous  copper  fairly  rapidly 
by  carbon  monoxide  but  the  reduction  of  cuprous  ion  to  copper 
is  comparatively  much  slower.  Oxygen  present  in  small  amounts, 
in  gaseous  mixtures  from  which  carbon  monoxide  is  to  be  re- 
moved by  absorption  will  prevent  the  precipitation  of  copper 
and  increase  the  capacity  of  the  solution. 

The  spent  ammoniacal  cuprous  liquor  after  leaving  the  absorp- 
tion system  is  regenerated  by  release  of  the  pressure  on  passage 
through  a  small  receiving  vessel  and  by  raising  the  temperature 
of  the  liquor.  The  vessel  may  be  worked  at  atmospheric  pressure 
or  with  a  partial  vacuum.  The  latter  is  preferable  from  the  point 
of  view  of  carbon  monoxide  removal,  but  the  ammonia  losses 

84  J.  Am.  Chem.  Soc.f  1921,  4Sf  1. 


188  INDUSTRIAL  HYDROGEN 

are  thereby  also  increased.  The  evolved  gas,  consisting  mainly  of 
carbon  monoxide,  is  freed  from  ammonia  in  a  water  scrubber  and 
may  be  returned  to  the  water-gas  holder  for  conversion  with 
steam  to  hydrogen  and  carbon  dioxide  in  the  water-gas  catalytic 
process.  In  general,  for  removal  of  carbon  monoxide  from  the 
ammonia  liquor,  temperatures  as  high  as  possible  without  decom- 
position of  the  solution  are  employed,  presumably  between  70° 
and  80°  C. 

For  hydrogen,  in  the  utilisation  of  which  high  pressures  are 
necessary,  this  method  of  removing  carbon  monoxide  is  probably 
the  most  economical  and  practical  yet  introduced.  On  the  other 
hand,  for  hydrogen  required  for  use  at  normal  pressure  it  is  un- 
doubtedly an  expensive  method,  since,  in  such  case,  in  addition  to 
the  actual  operational  expense,  the  cost  of  compression  must  be 
debited  to  the  process. 

Purification  by  Interaction  with,  Calcium  Carbide. — This 
process  is  widely  quoted  in  hydrogen  literature  but  is  not  prac- 
tised. The  process  is  recorded  as  a  result  of  the  Frank  patents.25 
In  these  patents  it  is  claimed  that,  at  temperatures  above  300°  C., 
passage  over  the  carbide,  of  hydrogen,  containing  carbon  mon- 
oxide, carbon  dioxide,  nitrogen  and  hydrocarbons,  results  in  the 
elimination  of  all  these  impurities.  Experiment  shows  that,  for 
practicable  speed,  the  temperature  of  the  carbide  must  be  con- 
siderably higher  than  300°  C.  Indeed,  analysis  of  the  claim  in  re- 
spect to  only  one  of  the  impurities  named  will  be  sufficiently 
illuminating.  It  is  common  knowledge  that,  in  the  cyanamide 
industry,  nitrogen  is  only  absorbed  readily  by  calcium  carbide 
at  temperatures  in  the  neighbourhood  of  800°-1,000°  C.  the  ni- 
trogen being  present  at  atmospheric  pressure.  At  such  tempera- 
tures hydrogen  purification  is  impracticable  owing  to  expense  of 
heating  alone,  even  if  the  reactions  quoted  proceeded  rapidly 
with  gaseous  impurities  present  in  small  concentrations.  The 
possibility  of  contaminating  the  hydrogen  with  acetylene  from 
the  carbide  is  an  additional  argument  against  the  use  of  this 

process. 

Purification  from  Methane. 

The  elimination  of  methane  impurities  from  hydrogen  is  not 
easily  accomplished.  The  stability  of  methane  and  its  dilution 
in  a  fairly  pure  hydrogen  both  render  its  removal  from  technical 

28  B.  P.  26,806/1906;  U.  S.  P.  964,415/1910. 


PURIFICATION  AND  TESTING  OF  HYDROGEN     189 

gases  difficult.  Fortunately,  in  the  majority  of  uses  to  which 
hydrogen  is  put,  methane  merely  acts  as  a  diluent.  This  diluent, 
however,  increases  steadily  in  concentration  in  a  circulatory  pro- 
cess, the  increase  finally  necessitating  a  constant  loss  of  hydro- 
gen as  a  "blow-off,"  in  order  that  the  concentration  of  methane 
and  other  inert  constituents  may  be  kept  within  limits. 

The  removal  of  methane  when  present  in  concentrations  of 
1  per  cent  or  less  is  attended  with  such  expense  that  it  is  gener- 
ally not  attempted.  The  methods  which  might  be  employed, 
however,  are  economically  more  feasible  with  the  "blow-off" 
gases,  in  which,  owing  to  consumption  of  hydrogen,  the  methane 
concentration  may  have  risen  to  10-15  per  cent. 

For  such  gases  there  are  two  main  possibilities  in  regard  to 
purification,  the  one  chemical,  the  other  physical.  The  chemical 
method  consists  in  bringing  the  methane-containing  hydrogen 
with  steam  into  contact  with  suitable  catalysts,  such  as  reduced 
nickel,  at  elevated  temperatures  (800°  C.).  Interaction  occurs  as 
previously  outlined  (Chapter  VIII) 

CH4  +  H20  =  CO  +  3H2. 

The  issuing  gas,  if  led  over  an  iron  oxide  catalyst  at  a  lower 
temperature  (500°  C.),  gives,  by  interaction  with  excess  of  steam 

CO  +  H20  =  C02  +  H2. 

If  the  hydrogen  is  being  produced  by  the  water-gas  catalytic 
process  the  latter  reaction  can  be  effected  in  the  catalyst  cham- 
ber normally  operating  on  a  water-gas  steam  mixture.  In  such 
case  the  subsequent  purification  would  be  as  described  in  that 
process  (Chapter  III  and  earlier  sections  of  this  chapter).  For 
other  types  of  hydrogen  production  a  special  catalyst  unit  would 
be  required  for  the  carbon  monoxide  conversion  as  well  as  for 
the  interaction  of  the  methane  and  steam.  The  economics  of  the 
purification  process  would  then  require  careful  consideration. 

For  gases  under  pressure  and  containing  a  relatively  high 
concentration  of  methane  (e.  g.,  10  per  cent)  the  physical  method 
of  methane  removal  is  worthy  of  note.  By  cooling  hydrogen  con- 
taining methane  in  a  liquid  air  cooling  mixture  to  —  184°  C.,  the 
partial  pressure  of  the  methane  in  the  gas  mixture  may  be  re- 
duced to  0.1  atm.,  the  partial  pressure  of  liquid  methane  at  this 
temperature.26  It  would  not  be  advisable  to  carry  the  cooling 

26Olszewski,  Compt.  rend.,  1885,  100,  940. 


190  INDUSTRIAL  HYDROGEN 

below  —  184°  C.  since  at  this  temperature  methane  freezes.  Its  re- 
moval from  the  cooling  coils  would  then  be  a  matter  of  difficulty. 
The  degree  of  purification  which  could  thereby  be  attained 
would  depend  on  the  pressure  of  the  original  gas  mixture.  The 
economics  of  the  purification  process  would  be  similar  to  that  of 
the  "liquefaction"  process  of  hydrogen  production  (Chapter  IV). 
It  would  therefore  only  be  applicable  when  large  quantities  of 
hydrogen  containing  marked  concentrations  of  methane  accumu- 
lated hourly  or  when  provision  for  the  cooling  process  was  at 
hand  for  other  purposes.  With  an  efficient  heat-exchange  sys- 
tem, it  should  be  observed,  80-90  per  cent  of  the  necessary  cooling 
could  be  provided  by  the  returning  gases  and  by  evaporation  of 
the  condensed  methane. 

Removal  of  Phosphine  and  Arsine. 

These  gases  may  be  present  in  silicol  process  hydrogen  and 
are  detrimental  to  balloon  fabric,  in  which  such  hydrogen  is 
normally  used,  and  to  iron,  copper  and  brass.  They  may  be  most 
readily  removed  by  passing  the  hydrogen  through  a  heated  tube 
containing  copper  turnings.  The  two  hydrides  are  decomposed, 
the  phosphorus  and  arsenic  combining  with  the  copper.  The 
quantities  of  impurity  present  are  generally  minute  so  that  the 
copper  can  normally  be  replaced,  when  rendered  inactive  by  inter- 
action with  the  gases.  Acid  salts  of  copper,  such  as  a  hydro- 
chloric acid  solution  of  cuprous  chloride  will  also  decompose  ar- 
sine  and  phosphine  with  the  formation  of  copper  arsenide  and 
phosphide.  It  would  be  necessary  to  conduct  this  reaction  in 
acid-proof  vessels  and  the  issuing  gas  would  require  scrubbing 
with  water  to  remove  acid  vapors.  Chromic  acid  could  be  sub- 
stituted for  the  acid  copper  salt.  The  impurities  present  would 
be  oxidised  in  this  case  to  arsenic  and  phosphoric  acids. 

Bleaching  powder  in  lump  form  has  been  suggested  as  an  oxi- 
dising agent  for  the  two  gases.27  The  introduction  of  chlorine 
compounds  into  the  gas  by  such  treatment  would  be  possible 
and  special  precautions  to  obviate  this  would  be  necessary. 

The  suggestion  by  Renard  28  that  the  gases  might  be  removed 
by  solution  in  petroleum  cooled  to  — 110°  C.,  while  practicable 

27  Wentzki,  Chem.  Ind.,  1906,  29,  405. 

28  Compt.  rend.,  1903,  136,  1,317. 


PURIFICATION  AND  TESTING  OF  HYDROGEN     191 

in  the  laboratory,  does  not  seem  to  offer  the  possibility  of  tech- 
nical application. 

Removal  of  Oxygen. 

Oxygen  may  be  most  readily  removed  from  hydrogen  by  com- 
bustion of  this  latter  gas  with  any  traces  of  oxygen  present, 
water  being  formed.  A  number  of  patents  with  reference  to  this 
have  been  filed.  The  combustion  can  be  effected  at  low  tempera- 
tures in  presence  of  catalytic  agents.  Knowles 29  claims  the  use 
of  platinised  asbestos  at  100°  C.  Reduced  nickel  is  operative  in 
the  region  25°-300°  C.,  the  temperature  varying  with  the  ac- 
tivity of  the  nickel.  It  is  therefore  apparent  that  in  the  methan- 
ation  process  for  the  elimination  of  carbon  monoxide,  traces  of 
oxygen  will  also  be  removed.  Hot  copper  and  glowing  platinum 
wire  have  also  been  used  for  a  similar  purpose. 

The  operation  is  quantitative  and  so  simple  in  any  case  that 
no,  difficulties  in  the  use  of  hydrogen  due  to  the  presence  of  oxy- 
gen ever  find  record.  It  should  be  observed,  however,  that  oxygen 
is  as  powerful  a  catalyst  poison  as  carbon  monoxide  in  many 
catalytic  processes.  Provision  should  therefore  always  be  made 
to  ensure  its  absence  from  gases  required  for  such  purposes. 

Removal  of  Water  Vapor. 

Gas  compression  always  reduces  the  percentage  concentration 
of  water  vapor  present  in  a  gas.  An  installation  of  a  drying 
system  is  therefore  preferably  inserted  on  the  high  pressure  side 
of  a  system  if  economy  of  drying  agent  is  to  be  sought.  As 
desiccating  agents,  granular  calcium  chloride  and  soda-lime  are 
the  technical  possibilities,  though  cooling  may  occasionally  be 
adopted  (Chapter  IV).  Physical  adsorbents  such  as  silica  gel 
are  finding  application.  With  solid  absorbents,  a  multiple  unit 
system  is  generally  adopted,  one  unit  being  continuously  out  of 
the  series  for  revivification  while  the  others  are  in  use.  In  such 
a  manner  continuous  desiccation  may  be  achieved. 

The  Testing  of  Hydrogen. 

(a)  Physical  Methods. — Hydrogen  with  a  single  impurity  in 
variable  concentration  may  readily  be  tested  by  means  of  an 

29  B.  P.  27,264/1910;  B.  P.  21,600/1911. 


192  INDUSTRIAL  HYDROGEN 

"effusion"  meter.  This  instrument  measures  the  rate  at  which  a 
definite  volume  of  gas  flows  through  an  orifice  of  standard  size. 
Since  the  velocity  of  effusion  is  inversely  proportional  to  the 
square  root  of  the  density  of  a  gas  or  gas  mixture,  hydrogen  dif- 
fuses the  most  rapidly  of  all  gases  and  an  impure  hydrogen  less 
rapidly.  Many  types  of  apparatus  based  on  this  principle  have 
been  constructed.  In  the  Schilling  meter,  of  German  origin,  a 
fixed  volume  of  gas  is  delivered  from  an  inner  glass  cylinder 
standing  in  a  solution  of  glycerine-water  contained  in  an  outer 
glass  vessel.  The  delivery  of  the  gas  occurs  through  a  standard- 
ised jet  which  is  one  of  four  exits  in  a  four  way  tap  fastened  into 
the  top  of  the  inner  cylinder.  The  other  exits  from  the  tap  are 
utilised  for  filling  the  cylinder  with  hydrogen  or  air  as  required. 
Two  marks  on  the  inner  cylinder  indicate  the  volume  of  gas,  the 
time  of  effusion  of  which  through  the  jet  is  measured  by  means 
of  a  stop-watch.  Standardisation  of  the  apparatus  can  be  made 
on  air,  tables  being  supplied  recording  the  air  time  for  various 
temperatures.  Such  standardisation  also  serves  as  a  check  on 
the  cleanliness  of  the  jet,  concerning  which  great  care  must  be 
exercised.  By  calibration  of  the  meter  against  samples  of  hy- 
drogen with  known  concentrations  of  the  single  impurity,  tables 
or  curves  may  be  constructed  from  which,  by  a  single  set  of 
measurements  on  the  gas  of  unknown  purity,  the  hydrogen  con- 
centration may  be  deduced.  Where  two  or  more  impurities  of 
varying  concentration  are  possible,  the  method  is  not  generally 
applicable  without  determination  of  the  impurities  and  their 
concentration.  In  such  case  an  effusion-meter  is  practically  use- 
less. In  one  special  case,  namely  in  " liquefaction"  hydrogen, 
the  use  of  an  effusion-meter  is  possible.  In  this  gas  the  impuri- 
ties are  practically  exclusively  carbon  monoxide  and  nitrogen. 
Since  these  gases  have  identical  densities  they  may  be  treated  for 
the  purposes  of  this  measurement  as  a  single  impurity,  thus 
enabling  the  purity  of  such  hydrogen  to  be  determined  by  such 
methods.  If  air  be  the  diluent  impurity  the  effusion  meter  is 
also  applicable. 

The  Simmance  Purity  Meter  constructed  by  Wright's  Gas 
Meter  Co.  of  London  is  a  more  rugged  apparatus  in  iron,  work- 
ing on  the  effusion  principle. 

Recording  apparatus,  for  hydrogen  with  a  single  impurity  of 
variable  concentration,  can  be  constructed  by  utilisation  of  the 


PURIFICATION  AND  TESTING  OF  HYDROGEN     193 

principle  of  buoyancy.  If  hydrogen  of  variable  purity  be  delivered 
at  constant  gas  pressure  to  an  aluminium  gas  holder  floating  in  a 
suitable  liquid  the  height  of  the  container  in  the  liquid  is  deter- 
mined by  the  density  of  the  gas  supplied.  By  attaching  the  gas 
holder  to  one  arm  of  a  sensitive  balance  and  providing  the  other 
with  a  pen  operating  on  a  chart  fastened  to  a  revolving  drum  the 
variations  in  buoyancy  and,  therefore,  in  gas  purity  can  be  re- 
corded. The  use  of  such  an  instrument  is  limited  to  hydrogen  ad- 
mixed with  a  single  impurity  or  to  a  number  of  impurities  which, 
owing  to  the  constancy  of  their  relative  concentrations,  are  equiv- 
alent to  a  single  impurity  in  respect  to  their  influence  on  density. 
Air  is  an  example  of  such,  as  is  also  the  nitrogen-carbon  monoxide 
impurity  of  "liquefaction"  hydrogen  previously  mentioned. 

A  method  of  hydrogen  testing  of  great  accuracy  which  can 
be  rapidly  operated,  and  can  also  be  used  with  recording  appa- 
ratus, is  based  on  the  principle  of  thermal  conductivity.  The 
thermal  conductivity  of  hydrogen  is  very  considerably  greater 
than  that  of  most  gases,  as  the  following  table  shows: 

Gas  kt  x  104  30 

Air  0.568 

Ammonia  0.458 

Carbon  monoxide 0.499 

Carbon  dioxide 0.307  . 

Ethylene 0.395 

Methane   0.647 

Nitrogen 0.524 

Nitrous  oxide 0.350 

Oxygen 0.563 

Hydrogen 3.27 

Helium 3.39 

For  an  historical  account  of  thermal  conductivity  methods  of 
gas  analysis,  reference  may  be  made  to  the  article  just  cited.  In 
reference  to  the  question  of  hydrogen  testing,  Prof.  Shakespear 
of  Birmingham,  England,  developed  a  "katharometer"  in  1915 
which  is  now  sold  in  England  by  the  Cambridge  Scientific  Instru- 
ment Co.  and  designed  to  sample  and  determine  the  amount  of 

80  kt  is  the  heat  In  gram-calories   flowing  in  1   sec.  through   a  distance   of 

1  cm.  per  sq.  cm.  for  1°  C.  drop  in  temperature.  This  table  is  cited  from  the 

Smithsonian  Physical  Tables  by  Weaver,  Palmer,  Frantz,  Ledig  and  Pickering, 
J.  Ind.  Eng.  Chem.,  1920,  12,  359. 


194  INDUSTRIAL  HYDROGEN 

air  in  hydrogen,  which  has  been  used  as  balloon  gas,  of  hydrogen 
in  air,  for  example,  in  the  sheds  used  by  airships,  and  for  like 
purposes. 

Shakespear's  apparatus  for  the  detection  of  hydrogen  in  air 
consists  of  similar  electrically  conducting  wires  arranged  in  cavi- 
ties in  a  metal  block,  one  of  the  cavities  being  closed  and  the  other 
communicating  by  small  perforations  with  the  atmosphere.  Cur- 
rent from  a  battery  is  passed  through  both  wires,  which  are  in- 
serted in  different  arms  of  a  Wheatstone  bridge,  a  balance  being 
then  secured  by  means  of  other  resistances.  Under  these  condi- 
tions the  heated  wires  remain  at  similar  temperatures  by  losing 
heat  at  the  same  rate.  An  alteration  in  the  proportion  of  hydro- 
gen in  the  air  will  cause  a  variation  in  the  heat  loss  from  the 
exposed  wire  of  which  the  change  of  resistance,  as  determined  by 
readjustment  of  the  bridge,  is  a  measure.31  For  hydrogen  con- 
taining air,  provision  may  be  made  so  that  the  gas  mixture  to 
be  analysed  flows  over  one  wire,  a  comparison  gas  having  a  con- 
stant composition,  such  as  pure  hydrogen,  and  having  a  thermal 
conductivity  of  the  same  order  as  that  of  the  gas  mixture,  pass- 
ing over  the  other  coil,  or  surrounding  it. 

The  method  has  been  extensively  tested  by  Weaver  and  his 
collaborators 32  and  has  been  utilised  by  them  for  the  determina- 
tion of  nitrogen  in  nitrogen-hydrogen  mixtures,  and  of  carbon 
monoxide  in  a  mixture  of  nitrogen,  hydrogen  and  carbon 
monoxide.  In  the  later  paper,  the  limitations  and  advantages  of 
the  thermal  conductivity  method  of  gas  analysis  are  discussed  in 
detail.  Reference  may  be  made  to  these  papers  for  detail  of 
the  procedure,  which  is  likely  to  find  extended  application  in 
hydrogen  technology  in  the  future. 

The  gas  interferometer  worked  out  by  Haber  and  Lowe  33  is 
similarly  applicable  to  variations  of  a  single  constituent  or  of  a 
single  constant  mixture  of  constituents  in  hydrogen.  The  appa- 
ratus can  be  made  very  sensitive  but  it  does  not  lend  itself 
readily  to  technical  usage  owing  to  its  cumbersomeness,  nor  can 
it  readily  be  made  an  instrument  of  the  recording  type.  Seibert 
and  Harpster 34  have  indicated  some  of  the  technical  possibilities 
in  the  use  of  such  an  instrument. 

81  B.  P.  124,  453/1916.     U.  S.  P.  1,304,208/1919. 

82  Loc.  cit.  and  J.  Ind.  Eng.  Chem.,  1920,  12,  894. 
88  Z.  ang&w.  Chem.,  1910,  23,  1,393. 

84  U.  S.  Bur.  of  Mines  Tech.  Paper  No.  185/1918. 


PURIFICATION  AND  TESTING  OF  HYDROGEN     195 

Attempts  have  been  made  at  the  suggestion  of  officers  of  the 
Royal  Air  Force  in  England  to  determine  the  purity  of  hydrogen 
by  acoustical  methods.35  The  velocity  of  sound  in  air  is  1,100 
feet  per  second.  In  hydrogen  it  is  as  high  as  4,100  feet  per 
second.  The  variation  in  the  two  gases  is  such  as  should  lead 
to  the  design  of  a  rapid  gas  tester.  As  yet  such  is  not  forth- 
coming. 

(t>)  Chemical  Methods. — Absorption  methods  of  hydrogen  es- 
timation are  delicate  and  unsatisfactory  for  technical  work.  Paal 
and  Hartmann  36  suggest  the  use  of  sodium  picrate  solution  con- 
taining colloidal  platinum  as  an  absorbent  for  hydrogen.  The 
process  occurring  is  one  of  catalytic  reduction  of  the  picrate  in 
presence  of  the  colloidal  metal.  In  principle  it  is  identical  with 
the  proposal  of  Hofmann  and  Schneider 37  who  employ  as  absorp- 
tion agent,  chlorate  solutions  containing  colloidal  osmium.  For 
such  absorption  methods  the  hydrogen  requires  preliminary  puri- 
fication from  impurities  such  as  carbon  dioxide,  hydrogen  sul- 
phide, oxygen  and  carbon  monoxide.  Moreover,  in  technical  hy- 
drogen these  gases  are  generally  present  in  small  amounts  and 
it  is  the  magnitude  of  these  impurities  that  is  generally  more  im- 
portant than  the  hydrogen  content. 

Combustion  methods  with  excess  of  oxygen  or  in  presence 
of  metals,  such  as  palladium,  or  by  metallic  oxides  such  as  cop- 
per oxide  are  applicable  to  hydrogen  estimation.  The  presence 
of  carbon  monoxide  must  be  determined  by  separate  meth- 
ods and  corrected  for,  if  high  accuracy  is  required.  Hy- 
drogen and  methane  can  be  estimated  in  the  same  mixture 
by  preferential  combustion  of  the  former  with  oxygen  in 
contact  with  palladium  or  with  copper  oxide  alone. 38  Methane, 
when  present  in  hydrogen  in  small  amount,  is  best  estimated  by 
complete  combustion  of  a  stream  of  the  hydrogen  with  an  excess 
of  oxygen,  the  carbon  dioxide  formed  being  then  determined  by 
weighing.  Allowance  for  any  carbon  monoxide  present  must  in 
this  case  be  made. 

For  the  estimation  of  carbon  monoxide  in  hydrogen  use  may 
be  made  of  a  modified  iodine  pentoxide  method  of  determina- 

35  Compare  : — Haber  and  Leiser.     «7.  /S'oc.  Chem.  Ind.,  1914,  S3,  54. 
38  Ber.,  1910,  ),3,  243. 
37  Ber.,  1915,  48,  1,585. 

18  See  Hempel ;  "Gas  Analysis,"  Richardt,  Zeitsch.  anorg.  Chem.,  1904,  S8, 
65  ;  Jaeger,  «7.  /.,  GwbeleucM.,  1898,  41,  764. 


196  INDUSTRIAL  HYDROGEN 

tion.39    At  a  temperature  of  160°  C.  carbon  monoxide  is  quanti- 
tatively converted  to  carbon  dioxide  according  to  the  equation: 

5CO      I0  =  5C0        I. 


25 


In  air,  by  means  of  this  reaction,  concentrations  of  carbon  mon- 
oxide as  low  as  0.001  %  may  be  readily  determined  by  absorption 
and  titration  of  the  iodine  formed.  With  hydrogen  containing 
carbon  monoxide,  some  reduction  of  iodine  pentoxide  by  hydro- 
gen results 

5H2  +  I205  =  5H20  +  I2. 

Consequently,  carbon  monoxide  in  such  mixtures  cannot  be  de- 
termined by  means  of  the  iodine  titration.  Instead,  the  iodine 
must  first  be  removed  by  cooling  and  passage  through  mercury, 
and  the  carbon  dioxide  estimated  by  absorption  in,  and  titration 
of,  standard  barium  hydroxide  solution.  A  word  of  caution  is 
necessary  relative  to  the  absorption  of  carbon  dioxide 
present'  in  small  quantities  in  hydrogen.  In  minute  con- 
centrations carbon  dioxide  will  pass  through  a  baryta  so- 
lution unabsorbed  unless  extreme  intimacy  of  contact  is 
attained  between  gas  and  liquid.  This  can  be  obtained 
by  the  use  of  a  centrifugal  stirrer  for  the  baryta  solution 
through  which  the  gas  is  bubbling.  It  is  well,  also,  to  employ  an 
excess  of  alkali,  estimating  the  excess  by  titration  with  acid. 
Methane  is  not  attacked  by  iodine  pentoxide  but  unsaturated 
hydrocarbons  must  be  removed  prior  to  the  determination.  This 
may  be  achieved  by  bubbling  the  gas  through  concentrated  sul- 
phuric acid  at  a  temperature  of  165°  C.40  The  presence  of  gaso- 
line vapors  in  the  gas  has  been  shown  by  Teague41  to  have  a 
very  deleterious  effect  on  carbon  monoxide  determinations  by  the 
iodine  pentoxide  method.  A  method  of  procedure  devised  by 
Teague  for  exhaust  gases  from  automobiles,  and  applicable  also 
with  minor  modifications  to  carbon  monoxide  in  hydrogen,  calls 
for  the  use  of  a  liquid-air  cooled  purification  tube,  which  will 
remove  from  the  gas  most  of  the  hydrocarbon  vapors,  including 
the  unsaturated  hydrocarbons,  water  and  carbon  dioxide.  With 
such  a  purification  good  results  were  obtained  on  a  complex  mix- 
ture. The  iodine  pentoxide  method  applied  to  hydrogen  gases 

"Levy,  J.  Soc.  Chem.  Ind.,  1911,  30,  1,437.     Graham,  ibid.,  1919,  38,  10  T. 
*°Weiskoff.     J.  Soc.  Chem.  Ind.,  1909,  28,  1,170. 
«  J.  Ind.  Eng.  Chem.,  1920,  12,  964. 


PURIFICATION  AND  TESTING  OF  HYDROGEN     197 

containing  carbon  monoxide  can  be  made  to  yield  an  accuracy  of 
0.01  per  cent. 

An  application  of  the  iodine  pentoxide  method  to  carbon  mon- 
oxide detection  and  approximate  estimation  was  developed  by  the 
Chemical  Warfare  Service  41a  based  on  the  development  of  a  green 
coloration  in  an  S03  — 1205  mixture.  This  apparatus  is  being 
placed  on  the  market  by  the  Mine  Safety  Appliances  Company  of 
Pittsburgh,  Pa. 

A  method  of  analysis  for  small  quantities  of  carbon  monoxide 
in  hydrogen  was  worked  out  by  Taylor  on  the  basis  of  the  Har- 
ger-Terry  process  of  preferential  combustion  of  carbon  monoxide. 
To  a  measured  volume  of  hydrogen  was  added  oxygen  or  air 
sufficient  to  oxidise  from  2  to  3  times  the  amount  of  carbon 
monoxide  presumed  to  be  present.  The  gas  was  then  passed,  in 
measured  amount,  over  an  iron-chromium  cerium  catalyst  at  230° 
C.,  and  the  residual  gas  bubbled  through  standard  barium  hy- 
droxide solution.  The  carbon  dioxide  formed  by  oxidation  of 
the  carbon  monoxide  was  then  estimated  by  back  titration  of  the 
baryta  with  standard  acid.  Operating  on  gas  mixtures  contain- 
ing 0.1  to  2  per  cent,  an  accuracy  of  the  same  order  as  that  at- 
tainable in  the  iodine  pentoxide  method  was  possible.  The  pro- 
cedure was  simpler  as  the  process  was  catalytic  and  no  compli- 
cations, due  to  imperfect  iodine  absorption,  were  possible.  Me- 
thane was  not  oxidised  in  the  process  even  when  present  to  the  ex- 
tent of  15  per  cent.  Precautions  were  necessary  due  to  the  absorp- 
tion of  carbon  dioxide  by  the  catalyst.  To  avoid  such  errors  as  this 
might  cause,  at  least  one  litre  of  the  gas  mixture  was  passed 
through  the  catalyst  chamber  before  the  actual  absorption  in 
baryta  was  started.  This  method  of  carbon  monoxide  estirr/ition 
was  afterwards  applied  to  the  automatic  carbon  monoxide  re- 
corder devised  by  Rideal  and  Taylor,42  in  which  the  preferential 
combustion  principle  was  combined  with  a  method  of  carbon 
dioxide  estimation  based  on  the  conductivity  of  lime  water  used 
as  an  absorption  agent.  This  recorder,  manufacture  of  which 
has  been  undertaken  by  the  Cambridge  and  Paul  Scientific  In- 
strument Co.  of  Cambridge,  England,  has  given  good  service  in 
the  estimation  of  carbon  monoxide  in  steam-iron  process 
hydrogen. 

«'aCf.  U.  S.  P.  1,321,061  and  1,321,062  to  Lamb  and  Hoover. 
« Analyst,  1919,   kk,  89. 


198  INDUSTRIAL  HYDROGEN 

Catalytic  agents  other  than  iron  oxide  catalysts  may  be  used. 
Prepared  copper  oxide  or  mixtures  of  copper  oxide  and  manganese 
dioxide  are  applicable  at*  100°  C.  or  even  lower.  Hofmann 
showed43  that  activated  copper  oxide  moistened  with  alkali,  or 
activated  copper  in  presence  of  oxygen  and  moistened  with  al- 
kali, also  oxidise  carbon  monoxide,  even  at  room  temperatures. 

The  estimation  of  oxygen  in  electrolytic  hydrogen  is  a  case 
which  is  peculiarly  suitable  to  the  thermal  conductivity  method 
of  estimation  previously  detailed.  Of  other  methods  of  oxygen 
estimation  applicable  to  recording  devices,  mention  may  be  made 
of  an  arrangement  employed  by  Rideal  and  Taylor.  Use  was 
made  of  a  carbon  dioxide  recorder  of  the  Simmance-Abady 
type,44  although  other  forms  of  carbon  dioxide  recorders  are 
equally  useful.  The  charge  of  gas  drawn  into  the  apparatus  in 
the  usual  way,  was  discharged,  through  a  heated  nickel  catalyst, 
to  the  absorption  system.  This  contained,  instead  of  the  usual 
potassium  hydroxide  solution,  a  quantity  of  water  which  served 
to  condense  any  steam  formed  in  the  catalyst  chamber  by  inter- 
action of  hydrogen  and  oxygen  and  also  to  cool  the  gases  to 
atmospheric  temperature.  The  residual  hydrogen  then  passed 
to  the  measuring  system  as  in  the  usual  manner  when  the  ap- 
paratus was  used  for  carbon  dioxide  estimation.  Since  the  re- 
action occurring  in  the  catalyst  chamber, 

2H2  +  02  =  2H20, 

(afterwards  condensed) 

results  in  a  diminution  in  volume  equal  to  three  times  the 
volume  of  oxygen  present,  the  readings  recorded  on  the  carbon 
dioxide  chart  when  divided  by  three  give  the  oxygen  content  of 
the  hydrogen.  Thus,  a  carbon  dioxide  chart  recording  up  to 
10  per  cent  of  carbon  dioxide  for  use,  for  example,  on  water- 
gas,  can  be  used,  with  the  stated  modification,  for  recording  .con- 
centrations of  oxygen  in  hydrogen  from  0  to  3.33  per  cent.  It  is 
obvious  that  it  may  be  similarly  applied  to  the  record  of  hy- 
drogen in  electrolytic  oxygen.  In  such  case  the  above  chart 
would  record  from  0  to  6.66  per  cent  of  hydrogen. 

Greenwood  and  Zealley 45  also  devised  an  apparatus  for  the 
automatic  estimation  of  small  amounts  of  oxygen  in  combustible 

"Ber.,  1918,   51,  1,334. 

44  Precision  Instrument  Company,   Manufacturers,  Newark,  N.  J. 

",7.  Soc.  Chem.  Ind.,  1919,  58,  871. 


PURIFICATION  AND  TESTING  OF  HYDROGEN     199 

gas  mixtures  or  of  combustible  gases  in  air.  They  used  heated 
platinum  wire  as  the  oxidation  catalyst  and  provided  their  appa- 
ratus with  a  means  for  giving  an  alarm  when  the  percentage  of 
oxygen  rose  above  a  certain  value.  It  cannot  be  claimed  that 
their  device  is  simple. 

The  detection  of  oxygen  in  hydrogen  can  be  simply  effected 
by  the  blue  coloration  imparted  to  colorless  solutions  of  cuprous 
salts  when  gas  containing  oxygen  is  bubbled  through  the  solu- 
tion. 

The  detection  and  determination  of  phosphine  in  hydrogen,  of 
importance  in  the  case  of  hydrogen  produced  by  the  silicol  pro- 
cess, has  been  thoroughly  studied  by  Soyer.46  For  detection,  the 
gas,  after  washing  with  water  and  removal  of  the  water  spray,  is 
burned  at  a  platinum  jet  and  a  porcelain  cover  is  brought  over 
the  flame;  a  green  coloration  indicates  phosphine.  Spectroscopic 
examination  of  the  flame  shows  clearly  three  phosphorus  lines. 
Alternatively  a  drop  of  water  suspended  in  the  loop  of  a  plat- 
inum wire  and  introduced  into  the  flame  for  1/15  second,  will 
contain  sufficient  phosphoric  acid  to  show  a  yellow  precipitate 
with  ammonium  nitro-molybdate.  This  latter  method  is  the 
basis  of  the  process  of  estimation.  The  products  of  the  com- 
bustion of  from  2  to  20  litres  of  the  gas  are  taken  up  with  water 
and  the  phosphoric  acid  estimated  as  phospho-molybdate.  With 
two  litres  of  gas  burned,  a  dilution  of  one  part  of  phosphine  in 
5,000  parts  of  gas  is  determinable.  With  20  litres,  a  concentration 
of  one  part  in  60,000  parts  is  measurable.  With  100  litres  of  gas, 
the  sensitivity  of  the  analytical  procedure  is  extended  to  dilutions 
of  one  part  of  phosphine  in  one  million  of  the  gas. 

Arsenic  may  be  estimated  by  the  usual  method  of  passing  the 
gas  through  a  heated  glass  capillary,  comparing  the  mirror  ob- 
tained with  standard  mirrors.  Sulphuretted  hydrogen  is  detected 
by  the  blackening  of  a  lead  acetate  paper  placed  in  a  T  tube,  at 
right  angles  to  the  path  of  the  oncoming  gas.  Approximately 
quantitative  results  are  obtained  by  comparison  with  standards, 
of  the  stains  obtained  in  a  given  time  with  a  given  gas  flow. 
Carbon  disulphide  may  be  similarly  detected,  after  the  passage 
of  the  gas  over  heated  platinised  pumice  or  reduced  nickel  at 
500°  C.  The  carbon  disulphide  is  thereby  caused  to  interact 

« Ann.  cMm.  anal.,  1918,  S3,  221.     Often*.  Atst.,  1919,  IS,  294. 


200  INDUSTRIAL  HYDROGEN 

with  hydrogen,  forming  hydrogen  sulphide,  which  can  then  be 
determined  in  the  usual  way. 

The  detection  and  estimation  of  acetylene  in  hydrogen  has 
been  standardised  by  Weaver.47  The  method  is  based  on  the 
formation  of  a  red  colloidal  solution  when  the  gas  is  absorbed  in 
ammoniacal  cuprous  chloride  solution  containing  0.025%  gela- 
tine, 0.125%  hydroxylamine  hydrochloride  and  50%  alcohol. 
Comparison  may  be  made  with  solutions  containing  a  standard- 
ised red  color.  0.03  milligram  of  acetylene  can  be  detected  by 
this  method.  Sulphuretted  hydrogen  and  carbon  dioxide  inter- 
fere with  the  estimation  and  may  be  removed  by  hot  alkaline 
pyrogallol.  In  the  gravimetric  determination  of  cuprous  acety- 
lide  it  was  shown  that  the  precipitate  should  be  washed  in  the 
absence  of  air. 

«J.  Am,.  Ch&m.  Soc.,  1916,  38,  352. 


Appendix  I 

A  complete  experimental  re-investigation,  by  Chaudron,  of 
the  equilibria  in  the  reactions 

3Fe    +  3H20  =  3FeO    -f  3H2 
3FeO+    H20=    Fe304  +    H2 
3Fe    +3CO   =3FeO    +  3C02 
3FeO+    CO   =    Fe3O4+    C02 

has  been  published  since  this  book  was  set  up  and  indexed.    (An- 
nales  de  Chimie,  1921,  16,  221.) 

This  research  represents  the  most  thorough  and  satisfactory 
work  which  has  been  performed  in  reference  to  these  reversible 
reactions.  As  the  data  obtained  in  the  research  remove  some  of 
the  difficulties  in  the  way  of  acceptance  of  the  earlier  data  they 
are  here  incorporated  in  the  book.  The  appended  diagram  shows 
graphically  the  results  obtained.  The  ordinates  represent  percent- 
ages of  the  reducing  gas  in  equilibrium  with  iron-ferrous  oxide 
and  with  ferrous  oxide- ferrous  ferric  oxide  at  various  tempera- 
tures plotted  as  abscissae. 


70O  8OO  900 

FIG.  XVI. 


000  1100 


It  will  at  once  be  noted  that  the  equilibrium  values  obtained 
vary  noticeably  from  those  given  in  Figs.  I  and  II  of  the  text. 

201 


202 


APPENDIX  I 


Especially  is  this  true  of  the  equilibria  involving  carbon  mon- 
oxide. 

The  results  obtained  give  direct  evidence  as  to  their  relia- 
bility. It  will  be  noted  that,  for  the  curves  involving  both  hydro- 
gen and  carbon  monoxide  as  reducing  gases,  a  triple  point  is  ob- 
tained (570°)  at  which  iron,  ferrous  oxide  and  ferrous  ferric  oxide 
coexist.  The  existence  of  this  triple  point  was  confirmed  by  ex- 
perimental test.  It  was  shown  that  ferrous  oxide  (which,  if  the 
diagram  is  correct,  is  unstable  below  570°)  slowly  changes  over 
to  iron  and  ferrous  ferric  oxide  when  heated  in  a  vacuum  at 
500°  C. 

The  reliability  of  the  experimental  results  is  confirmed  by 
the  process  of  combining  the  results  with  both  reducing  gases. 
Thus,  a  combination  of  the  equilibrium  ratio,  Kx^pjj  n/PH 
with  K2  =  PQQ  ./PQO  m  Presence  °f  the  same  two  solid  phases 
at  any  one  temperature  should  give  the  water-gas  equilibrium, 
PH0><PCO        Kl 


The  values  so  obtained  are  in  good  agreement  with  the  very  re- 
liable results  obtained  by  direct  measurement  of  the  gaseous 
equilibrium.  This  is  shown  by  the  following  table  which  gives, 
for  iron  and  ferrous  oxide  as  the  solid  phases,  the  individual  and 
combined  values  of  K±  and  K2  and,  in  addition,  the  corresponding 
calculations  for  the  water-gas  equilibrium  made  by  Haber. 


Tern- 
perature 

Ki=PH20/PH2 

K*=PC02/*CO 

K  =  KJK2 

K  (Haber) 

686° 
786 
886 
986 

0.47 
0.55 
0.65 
0.75 

1.37 
0.63 
0.51 
0.40 

0.34 
0.87 
1.27 
1.80 

0.57 
0.86 
1.19 
1.90 

The  new  data  do  not  make  any  substantial  difference  to  the 
general  conclusions,  based  upon  the  earlier  experimental  data, 
which  were  presented  in  the  introductory  section  of  Chapter  II. 
The  actual  figures,  however,  presented  on  page  44,  for  the  vol- 
umes of  hydrogen  and  carbon  monoxide  consumed  in  the  attain- 
ment of  equilibrium  conditions  in  the  presence  of  the  various 
solid  phases  will  be  altered  by  these  new  results.  Accordingly, 


APPENDIX  I 


203 


in  the  following  tables  are  presented  more  reliable  data  for  the 
several  equilibria. 

Fe304-FEO  REACTION. 


Temperature 

%  H2  Consumed 

%  CO  Consumed 

Water-Gas  :H2 

570° 
650 
750 
850 

27 
41 

58 
75 

47 
55 
67.5 
75 

2.7 
2.1 
1.6 
1.33 

FeO-FE  REACTION. 


Temperature 

%  H2  Consumed 

%  CO  Consumed 

Water-Gas  :H2 

570° 
650 
750 
850 

27 
30 
35 
38 

47 
44 
40 
36 

2.70 
2.70 
2.66 
2.70 

It  will  be  observed  that  the  new  results  show  the  Fe304  -  FeO 
cycle  to  be  less  favorable,  as  regards  water-gas  :  hydrogen  than 
was  previously  calculated.  They  demonstrate  the  advantage  of 
working  at  higher  temperatures  on  this  cycle  in  so  far  as  this 
water-gas  :  hydrogen  ratio  is  concerned.  The  relative  quantities 
of  water-gas  consumed  to  hydrogen  yielded  is  much  less  depen- 
dent on  temperature  in  the  case  of  the  FeO  -  Fe  cycle,  nor  is  this 
cycle  so  economical  as  regards  water-gas.  The  percentages  of 
hydrogen  in  equilibrium  at  the  various  temperatures  in  the  two 
cycles  during  the  steaming  phase  may  readily  be  obtained  from 
the  figures  in  the  second  column  of  each  of  these  last  two  tables. 


INDEX  OF  AUTHORS 


Abbott,  41. 

Abrest,   130. 

Adam,  100. 

Alt,  91. 

Altmayer,  148. 

American    Oxhydric   Co.,    109. 

Ardol,  Ltd.,  92. 

Armstrong,  163,  164,  171. 

Ashe,  167. 

Bacon,  156. 

Badische  Anilin  u.  Soda  Fabrik,  28, 

31,  52,  62,  65,  66,  69,  76,  77,  79, 

92,  97,  99,  158,  175,  176,  184,  185, 

186. 

Baggs,  27. 
Balfour,  29,  59. 
Ballingall,  35. 
Baly,  91. 
Barth,  155. 
Bates,  29,  37. 
Battelli,  123. 
Beaupre,  129. 
Bedford,  99,  176,  178. 
•  Bergius,  100,  123-127. 
Berk  and  Co.,  176. 
Berlin     Anhaltische     Maschinenbau 

Aktiengesellschaft,  41,  153. 
Blair,  52. 
Bosch,  41. 
Bray,  29,  59,  183. 
Brindley,  127. 
British  Oxygen  Co.,  29,  59. 
Brooks,  156. 
Brownlee,  155,  156. 
Buchanan,  66. 
Bunte,  23,  153. 
Burdett  Co.,  110,  117,  118. 
Burgess,  23. 
Burrell,  23. 

Carbonium  Gesellschaft,  157. 
Carpenter,  23,   161,   176. 
Caspari,  105. 
Chaillaux,  168. 
Chaudron,  25,  201-203. 
Clark,  156. 

Claude,  16,  94-96;  100,  178. 
Coehn,  105,  115. 


Compagnie  du  Gaz  de  Lyons,  65. 

Compagnie  Generale  d'Electro- 
chemie  de  Bozel,  138. 

Consortium  f.  Elektrochemische  In- 
dustrie, 132. 

Coward,  22,  23. 

Crosfield,  163,  164. 

Curme,  100. 

D'Arsondal,    108. 

Day,  18. 

De  Jahn,  186. 

Dellwik-Fleischer  Co.,  29,  45. 

Dempster,  37,  48,  58. 

Denis,  161. 

Dewar,  100. 

Dieffenbach,  29,  30,  63,  68,  86,  158. 

Dixon,  22. 

Donnan,  91. 

Dubosc,  161. 

Du  Motay,  81,  86. 

Eldred,  65. 

Electrolabs  Co.,  115,  116,  118. 

Elektrochemische  Werke,  Bitterfeld, 

160. 

Ellenberger,  81. 
Ellis,  65,  82,  155,  161. 
Ellworthy,  64,  65,  99,  100. 
Engels,  82,  83. 
Erdmann,  99. 
Evans,  42,  174,  176. 

Fairlie,  148. 
Falcke,  27. 
Falk,  22. 
Faraday,  102. 
Ferguson,  52. 
Fernbach,  165. 
Fischer,  91. 
Foersterling,  127. 
Fonda,  184. 
Frank,  155,  188. 
Frazer,  183. 

Garuti,  108,  109. 

Gauger,  23. 

Gautier,  99. 

General  Chemical  Co.,  186. 


204 


INDEX  OF  AUTHORS 


205 


Giffard,  27. 

Goldschmidt,  160,  162. 

Gordon,  139. 

Graham,  196. 

Greenwood,  83,  84,  198. 

Griesheim  Elektron  Co.,  63,  81,  84, 

87,  130,  179,  184. 
Griggs,  38,  40. 
Grimnes,  25. 
Guillet,  175. 
Gwosdz,  60. 

Haber,  16,  194,  195 

Hahn,  60. 

Hainsworth,  187. 

Harger,  58,  80,  180. 

Harpster,  194. 

Hartmann,  196. 

Hembert,  64. 

Hempel,  195. 

Henke,  81. 

Henry,  64. 

Hilditch,  163,  164,  171. 

Hills,  28. 

Hoffmann,  163,  195,  198. 

Hood,  176. 

Hooton,  169. 

Horine,  120. 

Hulett,  89. 

Huntingdon,  186. 

Improved  Equipment  Co.,  41. 
International  Oxygen  Co.,  110,  112, 
113,  114. 

Jacob,  27. 

Jaeger,  195. 

Jaubert,  57,  128,  132,  144,  167. 

Johnston,  63. 

Jouve,  99. 

Katz,  161. 
Knowles,  191. 
Koepp,  160,  161. 
Koester,  27. 
Krupp,  86. 

Lackmann,  161. 
Lahousse,  169. 
Lamb,  183. 
Lane,  28,  31,  32. 
Langer,  64. 
Latchinoff,  108. 
Leiser,  195. 
Leslie,  161. 
Lessing,  152. 
Lever  Bros.,  58. 
Levi,  82. 

Levin,  27,  115,  116. 
Levy,  196. 


Lewes,  27,  28. 
Lewis,  104,  147,  149. 
Linde,  186. 

Linde-Frank-Caro,  92-94,  97. 
Loewe,  194. 
Loewig,  66. 
Lowe,  155. 
Lowry,  89. 
Lunden,  30,  31,  57. 
Luttringer,  161. 

McElroy,  161. 

Machtolf,  157. 

Majert,  168. 

Marechal,  86. 

Maxted,  31,  46,  50,  51,  66,  171. 

Mayer,  148. 

Mazza,  100. 

Meade,  174,  177. 

Meister  Lucius  &  Bruning,  161. 

Merz,  82,  162. 

Messerschmitt,  28,  30,  37,  38. 

Moldenhauer,  29,  30,  63,  86,  158. 

Mond,  64. 

Monteux,  28. 

Moses,  41. 

Mueller,  65. 

Naher,  65. 

Nauss,  152. 

Neville,  88. 

Nitridfabnk,  G.  m.  b.  h.,  160. 

Norris,  161. 

Northrup,  167. 

Oechelhauser,  153. 
Oerlikon  Co.,  110. 
Olzewski,  189. 
Osaka,  105,  115. 
Ovitz,  161. 

Paal,  195. 
Payman,  23. 
Phillip,  127. 
Pictet,  157,  159. 
Piva,  82. 
Plenz,  23. 
Pompili,  108,  109. 
Pring,  148. 
Prins,  87. 
Pullman,  65,  99. 

Ramsay,  123. 
Randall,  147. 
Read,  64. 
Reilly,  166. 
Renard,  190. 
Ribau,  162. 
Richards,  107. 
Richardt,  195. 


206 


INDEX  OF  AUTHORS 


Richter,  168. 

Rideal,  49,  106,  115,  175,  181,  182, 

197,  198. 
Rieche,  161. 
Rincker,  154. 

Robertson,  23.  , 

Rogers,  122. 

Sabatier,  16,  126. 

St.  John,  152. 

Santos  Dumont,  15. 

Sarason,  130. 

Schaefer,  41. 

Schenck,  27. 

Schilling,   192. 

Schmidt,  109. 

Schneider,  195. 

Schoop,  106,  110. 

Schreiner,  25. 

Schriver,  110. 

Schuckert,  110. 

Schwartz,  168. 

Seibert,  194. 

Senior,  167. 

Shakespear,  193,  194. 

Shepherd,  18. 

Siedler,  81. 

Siegel,  54. 

Snelling,  99. 

Societe  Francaise  L'Oxylithe,  132. 

Soddy,  100. 

Soyer,  199. 

Speakman,  166. 

Spitzer,  41. 

Stern,  158. 


Taylor,  49,  175,  182,  197,  198. 
Teague,  196. 
Teed,  134,  138,  145. 
Teissier,  168. 
Terres,  23. 
Terry,  180. 
Thomas,  171. 
Thorsell,  30,  31,  57. 
Titus,  187. 

Uhlinger,  155,  156. 
United  Alkali  Co.,  161. 
Uyeno,  130. 

Van  Royen,  27. 
Vignon,  65. 

Weaver,  132-138,  142,  146,  193,  194, 

200. 

Weber,  184. 
Weise,  161. 
Weiskoff,  196. 
Weith,  82,  162. 
Weizmann,  165. 
Wentzki,  190. 
Wheeler,  23,  118. 
Williams,  176,  186. 
Wolter,  154. 
Wright,  192. 
Wroblewski,  73. 

Young,  123. 

Zealley,  198. 
Zeppelin,  15. 


INDEX  OF  SUBJECTS 


Acetylene,  detection  and  estimation 
in  hydrogen,  200. 

— ,  hydrogen  from,  157-158. 

Acids,  hydrogen  from,  169,  170. 

Alkali  formates,  decomposition  of, 
160-162. 

,  synthesis  of,  160-161. 

Aluminium-amalgam  hydrogen  proc- 
ess, 129. 

Aluminium-sodium  hydroxide  proc- 
ess, 145. 

Ammonia  synthesis,  hydrogen  re- 
quirements for,  16. 

Ammoniacal  copper  solutions,  purifi- 
cation of  hydrogen  by,  185-188. 

Analysis  of  hydrogen,  191-200. 

Aqueous  alkalis,  hydrogen  from, 
131-146. 

Aqueous  alkalis,  purification  proc- 
esses with,  184-185. 

Argon  in  nitrogen-hydrogen  mix- 
tures, 74. 

Arsine,  detection  and  estimation  in 
hydrogen,  199. 

Arsine,  removal  from  hydrogen,  190. 

Bamag-Bunte  process,  153,  154. 
Bergius  process,   123-127. 
Burdett  hydrogen  cells,  117-118. 
By-product    electrolytic    hydrogen, 
120-122. 

Calcium  carbide,  purification  with, 
188. 

Carbon  deposition,  steam-iron  proc- 
ess, 45. 
— , ,  prevention  of,  46. 

Carbon  dioxide  removal,  72,  73,  80, 
176-178. 

Carbon  disulphide,  removal  from 
hydrogen,  175-176. 

Carbon  monoxide,  catalytic  decom- 
position, 45. 

,  estimation  in  hydrogen,  195- 

198. 

,  liquefaction  of,  90-99. 

,  removal  of,  64-80,  90-99,  178- 

188. 

Catalytic  hydrogenation,  16,  179, 
180. 


207 


Catalysts  for  interaction  of  hydro- 
carbons with  steam,  158. 

Catalysts  for  water-gas  reaction,  64- 
69. 

Chemical  analysis  of  hydrogen,  195- 
200. 

Choice  of  hydrogen  process,  21,  22. 

Classification  of  production  meth- 
ods, 19-21. 

Claude  liquefaction  process,  94-96. 

Coal  gas,  hydrogen  from,  152-154. 

Contact  mass,  steam-iron  process, 
28-31. 

,  reduction  of,  42-48. 

,  steaming  of,  48-52. 

Cuprous  salts,  ammoniacal,  for  hy- 
drogen purification,  185-188. 

Dehydrogenation  processes,  hydro- 
gen from,  163-165. 

Dieffenbach  and  Moldenhauer  proc- 
ess, 86-89. 

,  mechanism  of,  88-89. 

,  theory  of,  63. 

Diffusion  processes  of  hydrogen 
preparation,  99-100. 

Efficiency  of  liquefaction  procesa, 
98-99. 

silicol  process,  144. 

steam-iron  process,  56-59. 

water-gas  catalytic  process,  75. 

Effusion  meters,  191-192. 
Electrolabs-Levin      Cell,      115-117, 

118. 
Electrolytic  hydrogen,  102-123. 

,  apparatus  for,  107-118. 

,  by-product,  120-122. 

Electrolytic  hydrogen  cells,  Burdett, 
117. 

Garuti,  108. 

International  Oxygen  Co., 
110. 

Levin-Electrolabs  Co.,  115. 
Schmidt,  109. 
Schoop,  110. 
Schuckert,  110. 
Electrolytic    hydrogen    production, 

theory  of,  102-106. 
,  operating  details,  119. 


208 


INDEX  OF  SUBJECTS 


Equilibria,  iron  oxides  and  carbon 
monoxide,  27. 

— ,  iron  oxides  and  hydrogen,  25- 
26. 

— ,  water-gas  reaction,  45,  46,  50, 
60,  61. 

— ,  with  steam  and  hydrocarbons, 
150-152. 

Estimation  of  impurities  in  hydro- 
gen, 191-200. 

Fermentation  processes,  hydrogen 
from,  165. 

Ferro-silicon  specifications,  for  hy- 
drogen production,  143. 

Field  processes  of  hydrogen  produc- 
tion, 127-130. 

,  aluminium  amalgam,  129. 

,  hydrolith,  128. 

,  metallic  solium,  127. 

Flow  sheets,  liquefaction  process,  91. 

,  water-gas  catalytic  process, 

74,  76, 

Gas  consumption,  liquefaction  proc- 
ess, 91,  98. 

,  steam-iron  process,  44-47. 

,  water-gas  catalytic  process.  75. 

Gas  interferometer,  use  of,  in  hy- 
drogen analysis,  194. 

Greenwood's  modification  of  Gries- 
heim-Elektron Go's  process,  84. 

Griesheim-Elektron  Go's  process,  80- 
86. 

,  mechanism  of,  82. 

,  patent  literature,  81. 

Griesheim-Elektron  Go's  process, 
purity  of  gas  from,  85. 

,  theory  of,  62-63. 

Harger-Terry  purification  process, 
180-183. 

Hydrocarbons,  hydrogen  from,  147- 
159. 

— f ,  theory  of,  147-152. 

Hydrocarbons,  interaction  with  car- 
bon dioxide,  151. 

— , steam,  158,  159. 

Hydrocarbons,  thermal  decomposi- 
tion of,  152-158. 

Hydrogen  from  acetylene,  157-158. 

acids,  169-170. 

alkali  formates,  160-162. 

aluminium   amalgam,   129. 

aluminium-sodium  hydroxide, 

145. 

aqueous  alkalis,  131-146. 

coal  gas,  152-154. 

dehydrogenation  processes,  163- 

165. 


Hydrogen  from  diffusion  processes, 

99-100. 

electrolytic  processes,  102-123. 

fermentation  processes,  165. 

ferro-silicon,  131-145. 

field  processes,  127-130. 

hydrocarbons,  147-159. 

Hydrogenite  process,  167. 

Hydrolith  process,  128. 

Lane,  process,  31-37. 

liquefaction  processes,  90-99. 

Messerschmitt  system,  37,  38. 

natural  gas,  154-157. 

petroleum,  154. 

sulphides,  169. 

silicol  process,  131-145. 

• sodium,  127. 

steam,  25-59. 

tar  oils,  154-157. 

volcanoes,  18. 

water-gas,  90-99. 

water-gas  and  steam,  60-89. 

Hydrogenite  process,  167,  168. 
Hydrogen  purification,  171-191. 
Hydrogen    sulphide,    removal    from 

hydrogen,  173-175. 
Hydrogen  supply,  sources  of,  18,  19. 
Hydrolith  process,  128. 

Ignition  temperatures  of  gases,  23. 
Inflammability  of  hydrogen,  23. 
Interferometer,  use  of,  194. 
International  Oxygen  Co.'s  electro- 
lytic hydrogen  cells,  110-114. 

Lane  generator,  32-34. 
Levin  electrolytic  cell,  115-117. 
Linde-Frank-Caro  process,  92-94. 
Liquefaction  processes,  90-99. 

Claude  process,  94-96. 

composition  of  gas,  96,  97. 

efficiency  of,  98,  99. 

flow  cheet.  91 

,  Linde-Frank-Caro,  92-94. 

,  plant  details,  97-99. 

Messerschmitt   hydrogen   plant,   37, 

38. 

Methane  from  carbon  monoxide,  179. 
— ,  hydrogen  from,  152-158. 
— ,  removal  from  hydrogen,  75,  152- 

158,  188,  190. 
Meteoric  hydrogen,  18. 
Multi-retort    generators,   steam-iron 

process,  31-37. 

Natural  gas,  hydrogen  from,  154- 
157. 

Nitrogen-hydrogen  mixtures  in  wa- 
ter-gas catalytic  process,  73. 


INDEX  OF  SUBJECTS 


Nitrogen  in  liquefaction  process  hy- 
drogen, 91. 

Nitrogen  in  spent  water-gas,  47. 

Nitrogen  in  steam-iron  process  hy- 
drogen, 50,  172. 

Nitrogen  in  water-gas,  47. 

Nitrogen  in  water-gas  catalytic  hy- 
drogen, 50,  172. 

Nitrogen,  removal  from  hydrogen, 
188. 

Oechelhauser  process,  153. 
Over-voltage,  hydrogen,  104,  105. 

oxygen,  104-106. 

Oxygen  detection  in,  199. 

—  estimation  in,  198,  199. 

—  removal  from  hydrogen,  191. 

—  requirements  for  preferential  com- 
bustion, 180. 

Petroleum,  hydrogen  from,  154-157. 

Phosphine,  detection  and  estimation 
in  hydrogen,  199. 

— ,  removal  from  hydrogen,  190. 

Physical  methods  of  hydrogen  prep- 
aration, 90-101,  102-123. 

Preferential  combustion  of  carbon 
monoxide,  180-183. 

Pressure  water  washing,  carbon  di- 
oxide removal  by,  80. 

Purification  of  hydrogen,  171-191. 

from  arsine,  190. 

carbon  dioxide,  80,  176- 

178. 

carbon  disulphide,  175. 

carbon  monoxide,  178-188. 

hydrogen  sulphide,  173- 

175. 

methane,  188-190. 

nitrogen,  188. 

oxygen,  191. 

phosphine,  190. 

water  vapor,  191. 

Reducing  gases,  steam-iron  process, 

42-48. 
Rincker   and   Wolter    process,    154- 

155. 

Safety  precautions,  22,  23. 
Silicol  process,  131-145. 

,  experimental  data,  132-139. 

,  ferro-silicon  specifications,  143. 

,  generator  problems,  136,  137. 

,heat  effect  in,  135. 

,  operating  details,  141,  142. 

,  plant  details,  139-141. 

,  sludge  disposal,  144. 

,  sodium  hydroxide  require- 
ments, 138. 


Single     retort     system,     steam-iron 

process,  37-41. 
Soda-Lime,  purification  of  hydrogen 

by,  183,  184. 
Sodium,  hydrogen  from  —  and  water, 

127,  128. 
Specific    heats    of    carbon    dioxide, 

carbon   monoxide,  hydrogen   and 

steam,  55. 
Spent  water-gas,  steam-iron  process, 

46,  47. 
Steam-iron  process,  25-59. 

,  aeration,  52. 

,  Bamag  plant,  41. 

,  contact  mass,  28-31. 

,  efficiency  of,  56-59. 

,  Grigg's  modification,  38-40. 

,  historical,  27,  28. 

,  Lane  generator,  32-34. 

,  multi-retort  type,  31-37. 

purification    of    gas,    51-52, 

171-191. 

,  purity  of  gas,  50,  51,  172. 

,  reduction  phase,  42-48. 

,scavenging  period,  49. 

,  single  retort  type,  37-41. 

,  steaming  phase,  48-52. 

,  thermal  balance,  53-59. 

,  water  -  gas  -  hydrogen   ratio, 

44-47. 
Sulphides,  hydrogen  from,  169. 

Tar  oils,  hydrogen  from,  154-157. 
Testing  of  hydrogen,  191-200. 

chemical  methods,  195-200. 

physical  methods,  191-195. 

Thermal   conductivity  of  hydrogen 
and  other  gases,  193,  194. 

Utilisation     of     hydrogen,     15,     16, 
,  future  possibilities,  17. 

Vapor  pressure  of  carbon  monoxide, 
92. 

nitrogen,  92. 

Volcanic  hydrogen,  18. 

Water-gas,  analysis  of,  61. 
Water-gas  catalytic  process,  64-80. 

,  carbon   dioxide   removal, 

72. 

,  catalysts  for,  64-69. 

,  catalytic  unit,  76. 

,flow  sheets,  74,  76. 

,  gas  compressors,  79. 

,  heat  interchanges,  77. 

,  operation  of,  69-74. 

,  outline  of,  64. 

,  plant  details,  76-80. 


210  INDEX  OF  SUBJECTS 

Water-gas   catalytic  process,  steam  Water-gas  consumption,  steam-iron 

consumption,  70-72.  process,  43-45. 

----  ,  theory  of,  60-62.  ---  ,  water  gas  catalytic  process, 

----  ,  water  compressor,  79.  ' 


,                              ,      .  TTT 

-,  water-gas,   hydrogen   ra-  $^f  equillbnum'   45'   46'   6°' 

-J™'  75<  Water-gas  reaction,  heat  of,  54. 

Water-gas  consumption,  liquefaction  Water  vapor,  removal  from  hydro- 

process,  98,  99.  gen,  191. 


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